# Which animal to breed to be a perfect assassin

What is the best choice when it come to deciding which animal to breed to be a perfect assassin?

The animal must be smart enough to understand which person to kill and which not to.

The animal must also be smart enough to find their victims.

How does it work? The government leaves an object hidden somewhere near the house of the victim, the object emits a smell or sound only the creature can hear from really far distances. The further the better.

The animal must be trained to understand kill commands through simple communication.

Example:

Show a blue scoop and the creature understands that it must kill every person in the house once it gets there.

Show another color it must understand that it must kill only the males or only the females and so on... Simple signals like that.

In order to tell the creature what, who and how many people to kill.

If it can work with vocal orders, even better.

So the animal needs to be smart enough to find signals from really far away and track down the house, be smart enough to understand basic communication and most important of all, be really fast at killing and really good at escaping.

If the animal can be trained to run away after a successful kill, even if injured, that's better.

An animal which can ignore pain and still run is preferred.

The animal should try to escape without being followed, if people are following it, it should be smart enough to not return to it's master until it is safe to do so.

Or better if the animal is stealthy enough to avoid being tracked down.

If possible, everyone should believe the animal is a demon sent from hell to punish sinners and when it disappears they will just think it went back to Satan.

So, which of the modern and ancient/extinct animals are the most suitable to being bred through generations into a creature perfect assassinations?

It does not matter if it's herbivorous or carnivorous, as long as it's good at killing.

The animal should not be too small, because it would be killed too easily.

• You have basically described a trained killer
– L.Dutch
Jun 3, 2020 at 19:19
• @Halfthawed: Species sapiens, with a lowercase initial and an ess at the end. It means "wise" in Latin; the plural is sapientes. There is no Latin word **sapien. Jun 3, 2020 at 19:53
• Are you limiting this to real creatures? Or are you looking for a plausible but fictional animal? (Because other than humans there really aren't many options for the "real" category)
– DBS
Jun 4, 2020 at 9:32
• I'm thinking that mice are highly trainable, fit through incredibly tiny cracks, and can hide anywhere. Give it a poison to put in food or rub on the target, and you're done. Jun 5, 2020 at 18:26
• sometimes the answer is "you can't" the number of constraints you have on the list means humans are the only creatures that qualify.
– John
Jun 6, 2020 at 22:48

What is the best choice when it come to deciding which animal to breed to be a perfect assassin?

Us.

Last time I checked, we are still animals:

The animal must be smart enough to understand which person to kill and which not to.

I don't want to start a political discussion here, and this makes me sad, but as a whole we seem too keen and too effective at profiling and killing people with as much specificity as you can imagine.

The animal must also be smart enough to find their victims.

Humans are very good at facial recognition. Few trainable animals are as good as we are. Seriously.

Our sight is not as good as that of some birds, but birds make poor assassins. I was going to add a [citation needed] joke here but just think of it: when a bird kills a person, it's news worldwide. But we have a whole industry that turns them into food for us.

Then we have beasts more properly equipped to kill humans like jaguars and bears, but we see more colors and finer details than they do. We could pick a target in a party much better than those animals could, and all we need is a picture. Most other animals would need a sample with the smell of the target, which is harder to procure.

How does it works? The government leaves an object hidden somewhere near the house of the victim, the object emits a smell or sound only the creature can hear from really far distances. The further the better.

The animal must be trained to understand kill commands through simple communication.

Example:

Show a blue scoop and the creature understands that it must kill every person in the house once it gets there.

Show another color it must understand that it must kill only the males or only the females and so on... Simple signals like that.

In order to tell the creature what, who and how many people to kill.

If it can work with vocal orders, even better.

With humans, as long as you are not hiring dyslexic people, you can get quite a good rate of properly followed commands.

So the animal needs to be smart enough to find signals from really far away and track down the house, be smart enough to understand basic communication and most important of all, be really fast at killing and really good at escaping.

If the animal can be trained to run away after a successful kill, even if injured, that's better.

We can totally do that and better:

Hathcock only once removed the white feather from his bush hat while deployed in Vietnam. During a volunteer mission days before the end of his first deployment, he crawled over 1,500 yards of field to shoot a PAVN General. He was not informed of the details of the mission until he accepted it. This effort took four days and three nights, without sleep, of constant inch-by-inch crawling. Hathcock said he was almost stepped on as he lay camouflaged with grass and vegetation in a meadow shortly after sunset. At one point he was nearly bitten by a bamboo viper, but had the presence of mind to avoid moving and giving up his position. As the General exited his encampment, Hathcock fired a single shot that struck the General in the chest, killing him.

I don't think any animal other than a human can be trained to be that single-minded.

An animal which can ignore pain and still run is preferred.

Give a man some cocaine and morphine, with the promise of more of these later, and not only you have a warrior that does not feel pain, you also have a very motivated warrior.

The animal should try to escape without being followed, if people are following it, it should be smart enough to not return to it's master until it is safe to do so.

Or better if the animal is stealthy enough to avoid being tracked down.

Hathcock crawled all the way back after killing that general two paragraphs ago.

If possible, everyone should believe the animal is a demon sent from hell to punish sinners and when it disappears they will just think it went back to Satan.

A killer who is stealthy enough can add some theatrics to their methods to make the gullible think the killings are paranormal. Some people do believe in the Yeti and the Moth Man up to this day.

So, which of the modern and ancient/extinct animals are the most suitable to being bred through generations into a creature perfect assassinations?

It does not matter if it's herbivorous or carnivorous, as long as it's good at killing.

I could post pictures of people killing people but that would be gory.

The animal should not be too small, because it would be killed too easily.

Counterargument: midgets are smaller targets.

• -1, because when someone in general sense refers to "animals", they mean non-humans, and not the biological classification "animalia". If someone asks how many animals are on the farm, would a sensible person count the people working there too? This answer might have been a funny comment, but no need for a full fledged answer which doesn't even answer what the OP was asking for. Wait, there is one already. So no need for this overly long joke.
– vsz
Jun 4, 2020 at 8:58
• @vsz: I would count all the farm animals, all the wild animals, pets, and all the earthworms in the fields, the horseflies, fleas and ticks on the livestock, the lice in the farmers' hair. I am a reasonable man however and would not count all the bacteria in the cow's digestive tract. Those guys are bacteria and not animals after all. Jun 4, 2020 at 10:11
• @vsz: I take this answer as a frame challenge, which is perfectly allowed. The answer goes to length to demonstrate that no other animal can satisfy the criteria. Jun 4, 2020 at 13:34
• Everyone here misses the point, especially the person calling it a mathematician's answer. Not only is this a valid answer, but story/universe-wise it makes a fabulous twist. You go through the story hearing about these bipedal beings that have been trained to kill so effectively, bred to kill, and then you find out that they're humans? Oof. Jun 4, 2020 at 18:24
• @vsz This isn't a mathematician answer by any means. This isn't about nitpicking - it is a perfectly valid answer that works well in-universe, presents minimal amount of extraneous premises to the proposed worldbuilding, and a way more believable answer than other alternatives. A mathematician answer's is useless. This is far from it. Jun 4, 2020 at 19:01

The animal you're asking for is known as Homo sapiens.

Sorry, but you're essential describing many actions which pretty much involve human-levels of intelligence,and the animals which have similar intellect will not be hard to notice (unless you're blind, though you'll still hear the death dolphin squirming towards you to do to you what it does to fish, or if you live in a place where it's common to find chimpanzees or crows inside of buildings).

But given that you're also including prehistoric creatures (which is NOT the way to go if you want intelligence. The mighty raptors Hollywood showed us could apparently be outsmarted by your average dog) and admitting both the classic meaning of animal as well as some impossible bioengineering in here (since you're willing to use breeding to achieve the traits you desire, plus you don't seem to mind bringing back extinct creatures, which could only happen through either this or a time machine), my bets on a non-human assassin animal would be on a genetically modified Giant Pacific Octopus.

Octopuses in general are in many ways nature's coolest assassins. They can't fly silently like an owl or slash you with claws like a lion. But it is known to be a very intelligent animal, can change both it's color and texture despite being colorblind, are stronger than a human and, one of the best: they can essentially fit inside any place larger than its beak, which is the only hard part of its body (so essentially any place larger than a penny will do). The giant pacific octopus, while also having many of these qualities, is larger and stronger than a human, and is known, like its fellow brethren, for being troublesome in aquariums due to their attempts (at times successful) of escaping their enclosures.

So let's see if this bioengineered Giant pacific octopus could fit the mold according to what a giant pacific octopus can already do without modifications:

The animal must be smart enough to understand which person to kill and which not to

Octopuses are capable of recognizing and remembering by sight and taste, so this is likely already doable with a normal octopus.

be smart enough to find their victims.

How does it work? The government leaves an object hidden somewhere near the house of the victim, the object emits a smell or sound only the creature can hear from really far distances. The further the better.

Otopuses have been shown to be able to transverse mazes, solve puzzles, and open jars with crabs inside by recognizing the food. Though I doubt smell or sounds can work, but if you have a layout of where the victim will be, making them go through a similar maze will let him learn where to go and how to come back. Also putting special fluids in the path it must go might also work, as it can taste its surroundings with its sucker pads.

The animal must be trained to understand kill commands through simple communication.

If it can work with vocal orders, even better.

Relying on voice won't work. They can feel variations in pressure with their skin, but that is for when they're underwater. Rather than colors (they're colorblind), showing special shapes might work decently well (show a crab sign and it could understand everyone must die) this one might require a bit more of bioengineering and conditioning to be properly tuned.

the animal needs to be smart enough to find signals from really far away and track down the house, be smart enough to understand basic communication and most important of all, be really fast at killing and really good at escaping.

Finding signs? No issue. Understand basic communication? I wouldn't say communication (especially not vocal), but it can understand signs and remember situations. Kill someone fast? Depends a bit, but since they can overpower sharks and humans alike, I see no reason why it couldn't learn how to quickly twist or break a neck, so not too crazy. Really good at escaping? Absolutely. Not only it can squirm inside places its potential pursuers could only dream to be able to access, it's ability to change color and texture can make it a challenge to see them in the first place (also many octopuses have poisonous saliva, with the blue ringed octopus being one of the most venomous animals in in the world, so with some bioengineering we can give it that weapon too).

run away after a successful kill, even if injured, that's better.

Many octopuses can heal entire arms in case they're lost (and at times will rip it off themselves in mating season), so clearly doable so long as there are enough arms left.

An animal which can ignore pain and still run is preferred

They can loose arms and escape and they can feel pain, it already happens in nature.

The animal should try to escape without being followed, if people are following it, it should be smart enough to not return to it's master until it is safe to do so.

This might be assured with some bioengineering, but given octopuses already have prey behavior and will camouflage and stay on low profile when chased by predators, it's clearly not a stretch (though I'd say den rather than master, as octopuses aren't quite social, but given that octopuses seem to have spatial memory it can likely avoid it's meeting point until it's safe).

If possible, everyone should believe the animal is a demon sent from hell to punish sinners and when it disappears they will just think it went back to Satan.

Well they look more like cthulhu than Satan. But since Chapodiphobia (fear of octopuses) already exists, I'm pretty sure such an assassin can easily leave people (and especially Japanese schoolgirls) terrified.

To summing it up, we have an animal that, at least in a way, can already do a variation of most of what you need it to, is considered to be extremely intelligent (one of the most intelligent invertebrates, which is still impressive despite what it's competing against), already capable of briefly leaving the water (some species are adapted to crawl around on land for short periods), can climb walls in some cases, if the surface is smooth enough to allow for the use of their suction pads (they're not capable of doing it indefinitely, but they're still strong enough to carry their 182 kg bodies vertically), have apparently preemptively killed sharks under fear of being attacked, are incredibly curious and are capable of learning by watching others (which is more of a big deal than it might sound).

So, with some adaptations to allow these animals to breathe and survive on land (maybe through a buffed up version of lungfish so that they don't completely loose their water breathing capabilities) and a boosting of their circulatory system to allow for a more active creature, as well as some boosting of their intellect and some modifications to the beak so that it's closer to a Humboldt squid's and maybe boost up its poisonous saliva to be as lethal as its blue ringed cousin's, we could essentially have a creature that, despite clearly sticking out like a sore thumb and not being the fastest one, is capable of adapting to situations, has incredible camouflage (let's hope the targets aren't fans of smooth surfaces though), can overpower a human, can fit into very small crevices and essentially disappear, could potentially recognize a target and look for the best strategy to attack and can remember about their surroundings, facilitating its escape.

Note:while I know octopuses aren't the smartest ones around and are clearly not adapted to living on land, I do believe they're one of the best fits for the "silent but deadly, hard to contain, cunning assassin" stereotype after us. The ideal scenario here would be to simply grant it a human's intelligence to maximize its effectiveness.

• octopus chimera assassin, very nice
– Kai
Jun 4, 2020 at 16:39
• I'm so glad to see I'm not the only person who immediately went to octopus. Also see en.wikipedia.org/wiki/Gravity%27s_Rainbow. Jun 5, 2020 at 2:19
• Dolphins and octopi. Aquaman approves of this answer. Jun 5, 2020 at 12:45
• octopi tend to leave very obvious trails on land.
– John
Jun 6, 2020 at 22:49
• +1 I love this! The killers should be sent in via the sewers to just pop up in the toilet bowl. That should be totally doable for even large octopodes. This will minimise time outside of the water and nobody would have any chance of seeing them coming... Also, this will easily satisfy the "supernatural" aspect. Victims strangled in the bathroom with the door locked from the inside... Doesn't get more "supernatural" than that. Jun 9, 2020 at 7:38

Mosquitoes would do admirably. All you need to do is mark the target with mosquito attractant.

Mosquitoes are the vectors for all sorts of lethal diseases, of which malaria is just the best-known. This is what makes them the deadliest creatures in the world.

Specially-developed assassin mosquitoes could carry a cocktail of existing diseases, or something new and more dangerous.

Mosquitoes are expendable and so return to master is not an issue.

Malaria deaths were traditionally believed to be caused by evil spirits or foul emanations (mal aria - bad air) so it fits your requirements exactly.

• Weaponized fleas work well too, provided that there isn't a James Bond clone around to distribute bug spray. Jun 4, 2020 at 15:50
• This was my first thought too, they're stealthy and already capable of killing. They're not so good at identifying targets visually, so it would work better if you had someone/something else mark the target with a specific pheromone and then send your seeker bugs in for the kill.
– bta
Jun 5, 2020 at 21:33
• @TheDaleks and bta: The Japanese actually looked into this, and found what both of you did. They aren't great at targetted kills, but they successfully used them to indiscriminately kill tens of thousands of Chinese during WWII by dropping them over cities. Jun 6, 2020 at 18:16

A poisonous or venomous snake? Your description sounds like a snake.

And it can be used as an assassination method as you describe, and Hannibal Barca kinda did use it to enemy ship. And it's quite common in my country when snakes hide inside the house, even I got visited by two snakes last month, and even if you have a dog or cat to protect you, they are more likely to die; either they get bitten themselves, or ingest the poison, or the venom goes through the wound when they bite the snake (we dont have veterinarians here). It cost me generations of my dogs, to the point where my monkey is better as a watchdog or alarm (I miss her, those two snakes came not long after my monkey was released back to the forest, and the recent one almost bit me in the leg) than my current dog which does nothing and just plays with his rock, but which lives longer compared to his predecessor, so natural selection I guess.

They can easily hide and ambush when the victim does not expect it, such as inside the shoes, or while sleeping and they get bitten; and they are quite slippery or agile and pretty fast. I advise you to put more than one though, and don't use the warning type or one that makes sound such as rattlesnake.

I can understand why explosive is not used in assassination, because that is just unnatural and too obvious, and makes a loud noise so a neighbor could wake up or notice, which is bad for assassination but works well for terror. Arson can work well enough without causing suspicion, but it won't work well for animal on fire since it's not natural too so it can cause suspicion.

I am not sure about how to control it, but maybe smell can do (but I don't know what kind of smell or chemical for it), and during winter they are more likely to hide inside warm clothing, and someone will probably need to wear that during winter.....

• Inland Taipans seem like a good way to go, as even the tiny newborns already have enough venom to kill an adult. Jun 4, 2020 at 12:13
• Just a minor correction - "Poisonous" would not be correct here - only venomous. Unless you expect the snake to assassinate by convincing the victim to eat it. Jun 4, 2020 at 15:00

## A cyborg beetle

Electric signals can be used to controll the movement of the insect. Add a small camera and a bit of software. Something like this:

import flight_patterns

import target_pictures

while active == True:

flight_patterns.outside()

if visual_input == target_pictures.target_structure:

flight_patterns.find_entry()

if environment == inside_building:

flight_patterns.search_structure()

if visual_input == target_pictures.target_face #alternatively target_ethnicity

fly to center of target_pictures.target_face

shaped_explosive_trigger = True


This is orders of magnitude more straightforward than your training idea. Additionally you can deployed swarms of these things, either to make sure someone really gets killed, or to cull a certain ethic or political group. Social media is a great source for target pictures and reasons to target people. You don't even need to search for targets yourself. Just train a maschine learning algorithm to pick pictures of everyone who attended say, a pride march or a KKK rally.

The Netflix show Black Mirror did something similar in the episode "Hated in the Nation. They used robotic bees, but cyborg synsects take advantage of the fuel and propulsion system insects provide.

There are some high-trainable killer-animals:

• Bears - top of the list. They are smart. They are fast. They are deadly. Unarmed person can do nothing to survive bear. They feel no pain in battle and can fight for hours being deadly wounded. But there are some problems. They are not a "ninja-style" and hard to control. Deploying killer-bears is quite a noticeable operation.They are very cowardly (Russian's proverb for soiling pants is "bear's disease"). And this bears would also be super-dangerous for it's own masters

• Dogs - are the most used killer-animals. When they are in a pack, dogs can target and kill ignoring almost any damage. In many countries execution with dogs was a routine. The only problem is that dogs are not good fighters. They are easy to harm and kill. Trained person with a stick or a whip can easily kill any dog one-on-one and keep a pack of 3-4 dogs away.

• Horses - are quite dangerous animals. They have instincts for battle - wild horses herds kill each other for territory and hunt predators. And that is the reason why horses are so good as war-animals (actually the best war-animal of all times) - they do actively participate in a fight. So battle horse is already a trained killer-animal. But it is hard to imagine assassin-horse. Clatter of hooves is not for stealth. But for an open fight horse is quite capable to execute kill command and return back for a carrot. Ponies are even better killers - they are much more aggressive

• Elephants - are smart, can lock on target and kill. They have a problem with rage and friend-or-foe recognition, but with some chemistry it can be controlled. But their size and weight is a huge problem!

• Large cats of different kinds (mostly of cougar kind and size). Seems to be a perfect assassins. But they are really hard to control. And they like to "play" - kill someone small just for "fun". They also quite vulnerable and cowardly. And they "work" alone at most (lionesses are an exception).

• Elephants are also incredibly quiet when they want to be - they have padded feet and can walk barely making a sound. But you'd still have trouble hiding one in a house. Jun 4, 2020 at 11:05
• @IndigoFenix One mustn't ignore the literal elephant in the room. Jun 4, 2020 at 15:51
• Horses are pretty cowardly, too. Someone who's familiar with horses would have zero problems scaring one off. Also, they don't have manipulative digits and they don't climb well or do well in small spaces... So you could just have a strong door with a lock, or a C gate in a tall, strong fence, or a room only accessible by ladder, and all of those would be completely safe. Jun 4, 2020 at 18:32
• Yeah it's weird, your blurb about horses makes me distrust pretty much everything else.
– pipe
Jun 5, 2020 at 5:38
• Horses are different (like dogs are). Some are cowardy working horses, some are aggresive war mashines. Someone who's familiar with horses would not try to scare brumby pony. Jun 5, 2020 at 11:26

You can always just implant a bomb instead of a microphone in an acoustic kitty or anti-tank dogs or use military dolphins for aquatic operations. There are also air borne options with pigeon guided missiles and incendiary bats

These aren't exactly what you asked for but I think they provide interesting thought fodder

Something like the indoraptor from Jurassic Park. if you are going to bring back extinct animals then obviously you can reengineer them. It was fairly intelligent and trainable with a targeting laser as seen in the movie. Training it to not eat everyone in sight may be a bit of a problem. It seems fairly tough but not bulletproof though. Then again what creature is bulletproof. Tranq darts don't seem to effective against it as well.

Hawks, eagles, and other raptors have wickedly sharp beaks and talons and are already used for hunting. Crows are quite intelligent, have excellent facial recognition, clever enough to use simple tools, and will act in a flock to harass larger creatures like the aforementioned raptors. It does not seem too terribly farfetched to me to breed/train a flock of birds that will both recognize targets when they see them and swarm/dive/peck until the target is dead.

I mean, it does seem a little farfetched, but less farfetched than anything else that's been mentioned so far. It seems to meet all or most of your requirements:

Targeted killings -- check, provided that you have images of the targets available.

Smart enough to find their victims -- check. Most birds can see quite well, over long distances, and a flock of birds even more so. If the flock is in the right general location, and the target goes outside, the flock will probably find him. I'm not sure if you could realistically train birds to spy through windows, but it's not like it'd be particularly unbelievable.

Fast at killing/good at escaping/will flee if injured -- check, at least when viewed as the flock as a whole. Individual birds aren't so good at fleeing when injured, especially if the damage is to their wings.

Escape without being followed -- yes and no. On one hand, training them to take a roundabout path is probably difficult, but on the other they can easily outdistance any ground-based pursuit.

Stealthy enough to avoid being tracked down -- check and double-check. It's not like a bird flying through the air leaves much of a trail to follow.

Everyone believes it's a demon -- check. Honestly, if a flock of birds started swarming and murdering people, I bet there are plenty of people today who would blame the supernatural even if the attack were caught on camera. It's just not a thing that birds do naturally.

If for narrative reasons you want to go with a single creature rather than an entire flock, I'd suggest a large eagle. They're fast (Wikipedia has max. horizontal speed at 80 mph and max. diving speed at 200 mph for a golden eagle), strong (for a bird), have good eyesight, and their talons are vicious enough that their handlers wear thick leather padding to prevent the bird from accidentally ripping their arm to shreds. Birds aren't so good at taking damage, but if you move fast enough, hit hard enough, and come at your target from literally out of the blue, that might not matter. I'm not sure whether eagles have the same facial recognition abilities that crows do, but other than that you seem good to go.

• I'm not sure how plausible it is to train a crow to use a poisoned weapon, otherwise that might work. If it can sneak in under cover of darkness, prick the target, leave the weapon behind and bug out... If it's sufficiently fast-acting that the victim dies before they can tell anyone what happened, it should look fairly demonic even if the murder weapon is found. After all, how did it get there? Jun 5, 2020 at 16:58
• Alternatively, if you can keep the birds from killing themselves, just coat their talons in poison and have them fly up in someone's face, scratch them, and immediately flee. That could seem pretty demonic; as noted, birds don't normally do that, and people normally don't drop dead in seconds from it. (Or use a slower poison so cause and effect is less obvious.) Jun 5, 2020 at 17:01

Not an animal, but robots, especially killer drones can be great at killing targets. They can be programmed to recognise faces, are very fast and lethal. They are not particularly expensive either and can be made in mass. I joined this community, just to post this answer :)

Chimpanzees. Easely the better animals to be able to handle all the coded knowledge you propose. Also by their similarity with humans will learn faster and retain better what techniques to use to kill.

They are strong.

Forth but not least, chimpancees have a very friendly image, they are slender capable of discretion and ambush, role-playing and deceit typical skills for assassination missions.

What I doubt very much is the animal will tolerate the pressure, maybe one particular animal could be suited among thousands unless you bread them selectively.

https://www.nytimes.com/2007/04/17/science/17chimp.html

• Very Planet of the Apes. This was my thought, too, or some sort of monkey bred for enough generations. Also go for breeding/engineering opposable thumbs. Jun 8, 2020 at 23:25

You examples limit the options greately.

• the animal must be clever enough to understand complex orders. Your examples are far from simple.
• it's not enough for the animal to be a killer. It has to know how to get to a guarded house, enter it, and leave. That requires patience and planning.

There are basically only two options - humans and hominids. I would personally select orangutans. They are very smart and have strength that is much superior to humans (they can tear your hand off). However, training them will still be much harder than training a human.

A falcon.

Falcons have a long history of being used to hunt creatures, and have been extensively bred already for hunting. They'd make excellent assassins.

To make them more lethal, you could add diseases to their beaks and claws which is fatal to humans but not falcons, so that a scratch from them would lead to death. This is a natural and normal thing, for animal attacks to give you diseases.

Rather than training them to kill based on commands (which is gonna be hard for any animal) you can train multiple falcons with particular triggers. One could be trained to attack anyone wearing a colour (like purple for nobility) one could be trained to go after scents, one could be trained to attack everyone in a building, another trained to kill people of a particular gender.

Assassins which have more types of falcon would be better paid, as they could slay a wider variety of targets.

They already attack on sight, so you can just leave an object which makes the smell of a mating falcon nearby to draw them in. They get spooked really easily, so they'll run away pretty quickly once the humans start getting agitated.

So, without using advanced genetic engineering, robots (or some variation), or humans, I think there is one animal that really fits the bill here.

Dogs

Yeah, not super original I know, but hear me out.

So, let’s go point by point shall we!

• Smart enough to know who to kill: Easy. Dogs have been trained to un-alive specific people since domestic dogs have been a thing. They’ve been used reliably in war, policing, and guarding for literally thousands of years, and are smart enough to hunt alongside humans without stealing the kill.
• Smart enough to find marked victims: Oh yeah, no problem here either. Dogs can be trained to do almost anything, including attack someone marked with a specific scent, or when they hear a specific tone. Combine that with an unbelievable sense of smell (watch the bloodhound Mythbusters episode) and very sensitive ears, they will have no problem finding marked prey.
• Trained to understand simple kill commands: Go watch a dog show and that can give you a pretty good idea of how well dogs can be trained. Dogs can understand many human words without training, can be trained to recognize thousands more, and can determine intent by tone, body language, and facial expression. Being trained to understand kill commands is easy. Going after specific people will take a bit more work, but dogs are smart, like scary smart. Seriously, I’ve owned dogs my whole life and several of them have been unbelievably intelligent. In one case I had an old dog whose teeth had gotten pretty flat, so when a dog growled at us she decided it would be easier to pin the other dog to the bed of the stream we were standing in and try to drown it. That’s more than simple defense that’s creative homicide. That’s human smart.
• Fast at killing: Wolves have a bite force of around 1200 lbs, that’s over 5,000 Newtons. Granted, domestic dogs are much more subdued, but the American Bandogge and Kangal breeds have bite forces above 740 lbs. Meanwhile, 5 lbs can collapse a throat. In addition to this fearsome bite, dogs are fast, really fast. Wolves top out around 37 mph, coyotes at around 43 mph, and greyhounds take the gold at 45 mph. A human’s very best, and I mean very best, is about 28 mph. You can not outrun a dog. You cannot out agile a dog, and perhaps worst of all, you probably can’t outlast a dog either. Dogs are also very good at stealth, as in a pack of wolves can completely surround you and you might never know until they attacked. In addition, grey wolves can hit 175 lbs, and the heaviest dog ever (a mastiff) was over 340 lbs! Lastly, dogs are pack animals, and almost nothing in the animal kingdom can take on a pack of wolves/dogs. Along the they are dangerous, but together they are a coordinated killing machine that would make lots of special operations teams jealous.
• Escape: Fast, quiet, and intelligent, escaping is not much of a problem. For example, if you have a Labrador Retriever, it is recommended that you have a fence that is at more than 6 feet tall, 3 feet in the ground, cannot be climbed, and has locks so that the door to the fence cannot be opened because they can open doors. Seriously, trained dogs make the raptors from Jurassic Park look tame in comparison.

To tie this all up, dogs are fiercely loyal to their owners, and can be bred to come in all shapes, sizes, builds, colors, and can be bred for a huge number of jobs. Seriously, mastiffs were bred to kill bulls for crying out loud. If you want a breed recommendation for something like this, something like a Rottweiler/Shepherd/Chow mix would do nicely. Rottweiler for size and a 375 lbs bite force, Shepherd for agility, intelligence, and ease of training, and Chow because of their aggressiveness, single mindedness, and toughness. Of course, that’s just one possible example, breed something more greyhound like for blistering speed, or more mastiff like for absolute brute strength. Which is the final advantage for using dogs for this, you can literally tailor make your perfect assassin dogs by nothing more than selective breeding, a process which doesn’t take long thanks to the fact that dogs are fully mature at 2 years old.

This has been a message from the Coalition For Being Nice To Dogs Because They Are Still Apex Predators Capable Of Killing You (and also because they are wonderful creatures), also known as CFBNTDBTASAPCOKY(aabtawc). Thank you

Since this includes biology and creature-design, why not use an uplifted, genetically engineered animal?

With sophisticated enough knowledge of bioengineering, it will be possible to A) create an intelligent creature that can and will understand commands, B) escape even if injured or in pain and B) likely escape unnoticed.

Let's expand on the octopus answer; scientists have made cells capable of doing simple computations (see https://news.mit.edu/2016/biological-circuit-cells-remember-respond-stimuli-0721), and assuming this cult/organization/whatever it is can do better, this octopus will likely be a biological supercomputer.

Since this means that the organization has knowledge of how brain structure works, they could then make these octopi perfectly obedient, instinctive killers. If that's not plausible enough, a special implant that releases dopamine when the octopus follows orders will work wonders (I say special because it'll need to be flexible or it'll impair the octopus's otherwise amazing flexibility).

Furthermore, with the right modifications, you can make creatures that look like Chthulhu. Toss in some octopus, some bat, and some chimp to your vat of genetic material and you have a less flexible and agile creature that will nevertheless be incredibly strong (overpowering targets with ease), capable of flight, and capable of wielding tools like a sniper gun.

If little Chthulhus are discovered killing people with human tools, A) that's going to make people think that eldritch horrors might, just might be real, B) that's going to freak the living daylights out of people and C) no one, and I mean no one in their right mind will risk assassination by Chthulhu.