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It is the year 2000 and Joe has committed a crime in a small town in central Europe. When the police calls all adults living in the area to voluntarily provide a DNA sample, Joe knows he's in trouble. He wants to fool the DNA test, but he doesn't understand much of the process. He has one week to come up with and implement a solution.

Joe knows from popular TV shows that a sample of his cells would be taken by swiping the inside of his cheek with a cotton swap. The cells would then be processed into a fancy diagram with small lines and if his diagram lines up with the one from the crime scene, he'll end up in prison (that's all Joe understands of the process).

DNA profile image source

Joe wants to coat the inside of his mouth with a substance that would produce different or additional lines on the diagram to "prove" that he is not the perpetrator. But he doesn't want to go all Hannibal Lecter and commit cannibalism to do so.

How would Joe try to fool this DNA test?

Answers should keep in mind:

  • Joe doesn't know enough about DNA profiling to be sure his idea would work. Asking another person (online or in person) is out of the question because it would lead to his suspicion.

  • It's the year 2000. The internet was a thing back then, but by far not as all-knowing as now. All solutions must have been available at that time (e.g. in a library or popular media, through anecdotal stories or widely spread missconceptions).

  • The solution doesn't have to actually work, but it must be plausible enough that a person with limited understanding of the process would assume it works. It must not be obvious (like having a visible amount of fresh blood in your mouth).

  • The solution must not require the commitment of a serious crime (like cannibalism even if that's technically not a crime). Burglary or deception is OK.

Answers will be rated by:

  • Ease of access to information (popular rumors will be rated higher than scientific papers)

  • Ease of access to materials (no exotic chemicals or materials a normal person wouldn't have access to)

  • Plausability. Whether or not the solution actually works is completely irrelevant for the rating, but it must sound believable.

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    $\begingroup$ If the question wasn't staged in 2000 it would have started a potentially paradoxical loop... since asking on Worldbuilding also count as "asking to other person" ;) $\endgroup$ – L.Dutch Jan 5 at 15:26
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    $\begingroup$ I'm obviously not Joe, so the universe will not get caught in paradoxical loops ;). I'm just having a hard time comming up with a plausible way to fool / fraud a DNA test that doesn't involve cannibalism, which doesn't fit the mood of my story at all. $\endgroup$ – Elmy Jan 5 at 15:33
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    $\begingroup$ Why not fake an Id and send some other person to do the test? $\endgroup$ – ghellquist Jan 5 at 20:46
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    $\begingroup$ Let me just say that Cannibalism is not a serious crime. Cannibalism isn't illegal, at least in the United States. The trouble starts when you try to do it because obtaining another person to eat involves breaking the law in most cases. If a friend voluntarily handed me his severed left leg and I decided to eat it, the law couldn't stop me (though I might be under investigation for a long time, as that's extremely suspicious behaviour). $\endgroup$ – user45266 Jan 7 at 2:23
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    $\begingroup$ Agh. What bothers me with this question is that a clever enough solution could be used to fool real criminal investigations >.<" $\endgroup$ – T. Sar Jan 7 at 12:06

14 Answers 14

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The movie Gattaca came out in 1997, so it is plausible that Joe has seen it.

The movie shows

an elaborate way to fool DNA test using biological samples from another human

Joe can the figure out that giving a deep French kiss (or some other intimate act involving exchange of genetic material) with someone else right before the test is taken might mix his DNA with the one coming from the other person.

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    $\begingroup$ Mission Impossible, 1996. Except this time the fake mask is inside your mouth. $\endgroup$ – Mazura Jan 5 at 23:39
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    $\begingroup$ You might want to French-kiss a person of the same sex as DNA profiling includes a sex-indicating test (according to Wikipedia) and having bothes sexes show up on the test might really set off the lab technician to have a closer look. Gattaca nit-pick: it just served to make the first test fail to force the blood-test which then could be faked the way the whole scheme is set up to do. $\endgroup$ – Ghanima Jan 6 at 18:11
  • $\begingroup$ Frenching somebody prior to the test might conceivably fail a DNA test. But it won’t fool it into detecting a different person instead. $\endgroup$ – Konrad Rudolph Jan 6 at 19:09
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The simplest way to fail a swab test is contamination of the sample. Eating something too soon before the test will do the trick.

Though what he really wants is the DNA of another human rather than a sample that comes back as beef cattle. These days there's an app for that, but in 2000 he'd probably have had to find a suitable bar to get himself a mouthful of human DNA sample*.

It's definitely the sort of thing a young man in trouble in the period would be told by his mates would work.


*If you don't know what I mean, ask your mum. No, I mean, no, don't ask your mum!

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    $\begingroup$ Ha! This could be funny. But how soon is "too soon before the test"? I guess inviting someone for a little fun right around the corner of a police investigation would be suspicious as well. $\endgroup$ – Elmy Jan 5 at 15:54
  • $\begingroup$ @Elmy, within an hour or so for eating something, I suspect you can use the same guidelines for other options $\endgroup$ – Separatrix Jan 5 at 15:55
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    $\begingroup$ Does this mean that if I eat a sausage, my mouth will have the DNA of a sausage? $\endgroup$ – kikirex Jan 5 at 23:11
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    $\begingroup$ @kikirex, that only works with wild haggis $\endgroup$ – Separatrix Jan 6 at 17:50
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    $\begingroup$ @kikirex Unfortunately I’m not sure I agree that this is an interesting question. The simple answer is: once the chain is broken down into individual nucleobases. This however doesn’t tell us much because even severely fragmented DNA (that is still DNA, and presumably present in sausage meat) won’t be usable in a DNA test. That doesn’t make it not DNA, it just makes it unsuitable for testing using a specific technology. $\endgroup$ – Konrad Rudolph Jan 6 at 19:21
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Hold something radioactive, to any degree, in or near his mouth for some amount of time at any point prior to the test.

"Radiation alters DNA" is a trope beyond question or examination for most people, and this was also the case in 2000. Especially given the weak understanding most people have about radiation and radioactivity there are a lot of things Joe might see on some blog and try out.

Pressing his face against a running microwave for a few hours? Worth it, to avoid prison. Eating lots of bananas? Sure! That's especially helpful if Joe is really set on coating his mouth with something (bananas are easy to mash up).

It won't work, of course. But it's plausible that someone like Joe might find information pointing to such a solution, or might assemble this plan from information he's able to run across on the internet. The idea being "it's still my DNA, but different from my actual DNA".

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    $\begingroup$ At first I thought "this is ridiculous", but depending on Joe's education, it's actually not too far fetched to be believable. I love the idea of him hugging a microwave and camping below a radio mast to "alter his DNA". $\endgroup$ – Elmy Jan 5 at 21:40
  • $\begingroup$ Oh man, you totally stole the general direction I was going to take this in, except you came up with better ideas. Oh well... $\endgroup$ – conman Jan 6 at 19:35
  • $\begingroup$ @Elmy In terms of terrible ideas that don't actually work, there is serious precedent for this sort of thing in real life, and it even inspired a large amount of research into human psychology. For the curious read up on McArthur Wheeler (medium.com/@littlebrown/…) and the dunning-kruger effect (en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect) $\endgroup$ – conman Jan 6 at 19:38
  • $\begingroup$ Actually radiation does not "alter" DNA; it chops it up — or "fragments" — the DNA. And since DNA profiling — as a step in its process — fragments the sampled DNA, Joe's scheme is entirely doomed to fail even of he irradiated himself to ARS-induced death. And in any case, if Joe ain't that bright 1) he will not be able to get hold of radioactive materials and 2) he is more than likely to think that chewing on radioactive materials is much worse than getting caught. $\endgroup$ – MichaelK Jan 7 at 12:41
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    $\begingroup$ @MichaelK Good lord. I am well versed in genetics, microbiology, and the relevant chemistry (including damage from radiation of varying kinds). The question is not "what would work?", it's "what might someone like Joe do in this situation?". It's not hard to imagine Joe stumbling across a blog that mentions bananas are radioactive, and another implying that radiation can "change" DNA, and then forming a desperate plan. Joe's success or doom is irrelevant to the question, and the whole point is that he doesn't have the information to understand these "plans" in detail. $\endgroup$ – Upper_Case Jan 7 at 16:33
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Step 1:

Line his mouth with something to keep the swab from hitting his actual tissue. It would help if he knew if it would be a cheek swab or a palate swab. A retainer would work on the latter. The former is a bit harder, but not impossible. Think flesh colored cloth. Or bite wings used to hold the teeth in place prior to dental x-rays. Or a cut up dental dam (or condom) carefully placed in the mouth.

Step 2:

Put someone else's saliva into his mouth. The easiest way to do this without asking for help, would be to find someone's abandoned (but recently used) plastic water bottle with a couple sips left in it. There would be plenty of backwash.

Step 3:

Put in the blocking material. Sip the remaining water and hold in the mouth as long as possible. Don't swallow at all. Let excess water drip down the throat or spit it out. It would not be unreasonable for someone to sip water just before getting swabbed, since opening a dry mouth while someone pokes around in there is uncomfortable. He'd have to time it well.

Will this work?

Maybe.

There are 3 basic ways to collect DNA for testing: Saliva (requiring a fair amount; it can be done with far less, but not reliably), blood, and cells from the inside of the mouth, usually the cheek. (There are other methods such as from dead bodies, bone marrow, forensic from hair, dried spit, etc, and from amniotic fluid, but none of these are relevant in this case.)

I think it would be hard to eliminate his own DNA from the sample. But probably easy to contaminate the sample with someone else's.

But given that you're looking for what your character thinks will work (or is his best chance at working), this is it.

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  • $\begingroup$ Would the person responsible for swabbing really not notice any of that? $\endgroup$ – Azor Ahai Jan 5 at 19:08
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    $\begingroup$ @AzorAhai Depends. A carefully cut out and placed piece of rubber could go unnoticed. A clear retainer probably would. If "all adults" are being called up to provide samples, the testing centers are going to be slammed. Unless it's super obvious, no one is going to be peering in anyone's mouth or checking things out. You take an extra long q-tip, say "open", swab, stick it in the tube with the right label. Next! Also: the question asks what will the character think will work, not what will actually work. $\endgroup$ – Cyn Jan 5 at 20:10
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Joe may consider to send someone else with his ID to the hospital where the test samples are taken. The medical personnel usually does not question someone's identity when showing the valid invitation for sample taking and also they do not have sufficient experience of an ID check.

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    $\begingroup$ I suspect this is the only sure-fire way to do it. So long as the fake ID holds up. Plot twist: The drifter Joe hires to take the DNA test for him then goes out and kills someone, and Joe is arrested because 'his' DNA is found at the second crime scene. $\endgroup$ – GrandmasterB Jan 7 at 4:06
  • $\begingroup$ The first person to be charged on DNA matching followed this procedure to get past mass screening by police. (en.wikipedia.org/wiki/Colin_Pitchfork) Then his stand-in talked too much in front of a barmaid... $\endgroup$ – DJohnM Jan 7 at 5:46
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Joe burgles a blood bank before he commits the crime (“burglary or deception is OK”). At the scene of the crime he spills plenty of stolen blood. The swabs taken from the scene of crime will contain far more DNA from random blood donors than from Joe, so when the forensics people amplify whatever markers they were using in 2000, Joe-derived template DNA will be out-competed in their PCR reaction by template from random blood donors. The forensics people will therefore have nothing to connect Joe to the scene of the crime.

By the year 2000, they probably weren't relying on Southern blots any more, but that shouldn't make any difference. If they do run a Southern blot (labeled DNA amplified from the crime scene probing a blot of Joe's DNA?), it's unlikely to hybridize more strongly to Joe's blot than to their control blots. If they sequence their crime-scene amplicon, it's not going to match the corresponding amplicon direct from Joe since Joe's signal in the crime-scene swab is swamped by the random blood donors' signals.

Other plausible sources of decoy DNA apart from burgling a blood bank? He could wander round a hospital in a borrowed white coat, and exfiltrate some fresh clinical waste from somewhere between operating theater and incinerator. Blood from a butcher's shop would be OK as the decoy if the forensics lab's PCR primers bind to sites that are conserved between humans and sheep/cattle. I don't know if this is the case (or was in 2000), but the primers must obviously have targets that are non-variable within the human population (they flank the variables regions), so perhaps it would work...

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  • $\begingroup$ "a sample of his cells would be taken by swiping the inside of his cheek with a cotton swap": if the lab technician draws out a cotton coated with blood instead of saliva, it could raise suspicion more than anything else. $\endgroup$ – kikirex Jan 6 at 19:25
  • $\begingroup$ @kikirex: I think you missed the point of this answer. Rather than trying to contaminate or spoof the sample the police take from him during the investigation, this is a suggestion that Joe should preemptively contaminate the crime scene with lots of other sources of DNA. So while the cheek swab will get his real DNA when they test him later, they won't be able to match it to the crime scene as the traces of his own DNA he left there will be drowned out by the contamination (e.g. blood from the blood bank). $\endgroup$ – Blckknght Jan 7 at 6:21
  • $\begingroup$ @Blckknght Oh, I missed the "preemptively" part. If this is the case, this is brilliant and unexpected. Edit: as I re-read the original question, I don't see any kind of malice beforehand: "Joe has committed a crime" and then "the police calls all adults to voluntarily provide a DNA sample". Maybe Joe didn't intend to commit a crime at all in the first place? $\endgroup$ – kikirex Jan 7 at 13:23
  • $\begingroup$ @kikirex: sure, this answer isn't an exact match for the situation asked about in the question (where Joe doesn't know to expect DNA testing until after the police announce it). So it might not help at all. But the situation where it does help is perhaps close enough to the questioner's scenario that it could still be useful. Maybe Joe's a low-rent hitman and tries to hide any evidence of his presence at a murder scene by dousing everything with pig blood. Could make for an interesting story! $\endgroup$ – Blckknght Jan 7 at 19:07
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Fooling the test is an utterly stupid idea to begin with

If you fool the test insofar as the result will be unusable, you will be asked to do it again. If the result is again unusable, you are highly suspect (probably after the first time already, anyway).
If you fool the test insofar as to show someone else's DNA, you are likely to be caught because there's a good chance the other person is undergoing, or will (at some undetermined point in the future) be undergoing the same test.
Also, whatever crimes the other person has already committed or will commit, you will be linked to them. Also, it's a felony to cheat on the test (whereas not doing it isn't).

Not complying is a viable (although tedious) option. I'm talking out of experience because I've been in that exact situation in 2000. Well not the exact situation, as I didn't commit the crime. But close enough anyway.

If you are in a place like, I don't know, China (?) then you are probably out of luck, but the question says Central Europe.

Central Europe means police asks and you say "no". Per Article 11, European Convention No. 5 (which is legally binding in all states), this means you are innocent unless police can prove something different. They can't, unless there is a witness or other evidence (obviously there isn't or they wouldn't do a mass screening) or unless you comply. So well, don't comply. "Doctor, it hurts when I do this. -- Don't do it."

The Convention 5 is fundamentally legally binding in all European states (and even some non-European ones) since early/mid/late 1951 / early 1952, depending which state exactly it is and on how fast the respective government was at declaring so.

The mere fact that police is trying to pervert the legal system to something which is similar to what we had in the Third Reich (proof of innocence instead of proof of guilt) is reason enough. By complying you give up your fundamental rights and subvert the system that is meant to protect you and other citizens from haphazard persecution. This should be reason enough for anyone to say "No". Unluckily, that's not the case. People take liberty as granted, but are not willing to make sacrifices to defend it.

Of course, being innocent (in real and by the law) doesn't mean you will be treated as innocent. Police tries to argue you into complying -- you have the chance to prove your innocence (which is really perverse because you have no need to prove your innocence, they need to prove your guilt). You say no.

Police keeps telling you there's only so-and-so-few suspects remaining, and then that there's only a handful remaining and you had better comply because they're already closing in on you anyway. You get letters, you get phone calls. One after one, they bully every non-complier into submission with this procedure. You say no.

Police starts showing up in your neighbourhood and at your workplace (yes I am not joking), doing what they can do to allege you are a culprit without explicitly saying it. They poke in every hole, try to find something, anything, whatever. They don't.

You file a complaint. Police says they never showed up, but if they did, then they'd be careful not to allege anything. Well, that means those people who told me police made allegations to them probably made this up. Funny how my neighbour knew I didn't do the test in the first place, he must be a psychic.

So, finally, after filing a complaint, you never hear of it again. Seriously, that's it. End of story.

17 years later, the guy who did it has died of old age, and his daughter finds body parts in some barrel in his cellar or garage (or whereever it was). It's in the newspapers, but you never hear as much as an excuse from police for having been falsely accused.
But whatever, as long as you never hear of them again, what do you care.

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  • $\begingroup$ Thank you for your heartfelt answer, but if I was in such a situation, I would have asked a lawyer. This is about a fictional character who committed a fictional crime and his crazy plan to fool the test is supposed to add a funny interlude to the story. $\endgroup$ – Elmy Jan 6 at 13:48
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    $\begingroup$ This doesn't answer the question. Joe wants to get off the list of suspects, not move up the list. Remember, Joe actually committed this crime, so there might be more evidence if the police looks closer at him. He might be legally innocent, but every suspect is legally innocent. That's because you stop being a suspect at the same time you stop being innocent, which is after your trial. $\endgroup$ – MSalters Jan 7 at 13:37
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What about a late identity-theft attack? Joe may switch the samples on their way to the lab. He can figure someway to replace the tag labels of a few samples including his own. This way the case would end up with a suspect - definitely not Joe - who will be jailed and close the case for good.

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See the episode of South Park (Season 21 Ep 3) where Randy wants his DNA sample to be that of a native American, and when the 23andme people come knocking on the door because of an inconsistency in his first sample he tells them to wait a minute and runs around South Park to find the Indian and gives him a deep French kiss to then run back to the people and give them a corrupted sample. Hope this helped.

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  • $\begingroup$ I mean this is an... interesting idea, but I don't this is as scientifically rigorous as the asker is wanting. $\endgroup$ – The Great Duck Jan 5 at 19:32
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    $\begingroup$ @TheGreatDuck, it's another version of the plot from Gattaca that L.Dutch mentioned $\endgroup$ – Separatrix Jan 5 at 20:00
  • $\begingroup$ Joe would have to be comically stupid to really believe this would work. It doesn't seem possible that he would attempt this. $\endgroup$ – user45266 Jan 7 at 2:28
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Chew hair.

Joe would feasibly have seen TV or movies where a strand of hair is used to identify someone.

He thinks therefore that it can also be used to be a source of alternate/confusing DNA and can pinch a strand from a co-worker's jacket.

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    $\begingroup$ I like this. It's believable to Joe, and it's simple. $\endgroup$ – user45266 Jan 7 at 2:33
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I'm assuming that there's some fictional textbook, far-fetched (potentially farcical in complexity) answer with a reasonable success rate which involves lining the mouth with plastic/wax and covering with another sample. However, with the given premise that Joe isn't an expert (and may not ask an expert) I'd find it more feasible to have a "best guess" solution from Joe. A solution however that could - even on the periphery of probability work.

Joe's Reasoning

So "being Joe" for a moment:

  1. I must provide a sample garnered from another human being; showing up on the test as "feline" would be an evident dodge and is probably as likely in resulting in his arrest as a positive match.
  2. Preferably I would want to provide a sample from someone who is the same gender and race as me. It is most likely that visual observations would be taken by the testers when the sample is conducted (in part to thwart this type of evasion); if I show up as "White, Female" and I'm a Afro-Caribbean male then that's going to be a dead giveaway and an evident dodge.
  3. It would be less than desirable to simple contaminate/sully the sample garnered; again this is likely to result in a re-test and arrest.

Method 1

Given those lines of reasoning, I (Joe) would visit a gay bar and pick up a man who happens to be the same race as me. (Being 2000, the general populous isn't as open minded, but it is legal and I would know where to go, even if I didn't frequent them myself). I would try to do this on the evening before the test day, then put effort in to ensure he stays the night and doesn't slip out a long time before the test; make him some bacon and eggs, suggest he stays in bed a while, etc. As close to the test as possible (assuming it's a home-visit?), I'd passionately kiss my new partner (however abhorrent I might find it; it's possible I'm averse to members of my own sex in that way).

Now I appreciate that it's unlikely this method would work, however as you request it's not the success; it's the plausibility; access to materials; non expert-info. To me (Joe), it's a plausible attempt at dodging the test that I could have engineered myself. It's also a touch dramatic that I'm willing to engage a sexual partner of my own sex if I've never done that before, in order to overcome this challenge.

Method 2

Further research on this (yet not beyond the potential realms of Joe's reasoning; something he could garner easily from rumour), one of the main ways to dodge a test is to simply have someone else take the swab: https://www.alphabiolabs.co.uk/learning-centre/can-someone-cheat-a-dna-test-2/

Now whilst Joe can't (them knowingly) involve anyone else, a higher chance of success may be appreciated if Joe disappears off with the swab in his hand for a moment, to take the sample from his still-sleeping partner (if the test was a home visit, early in the morning - something he would know in advance). NB. Evidently the officers conducting the test would have not followed "textbook regulation" by allowing Joe to leave their sight with the swab, but then - it's first thing in the morning - one of the officers is still hung over, and the other is a trainee! - I'm sure this could be explained off somehow.

Method 3

An alternate method 2, bit wacky but follows the rules; Joe previously worked as a magician's assistant whilst taking a gap year from university, and learned sleight of hand. He takes a swab of his sleeping partner before the officers arrive and switches it with the test swab.

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    $\begingroup$ Depending on how open-minded Joe is, giving his one-night stand a blow-job the next morning might be better. Especially if he then rubs the semen around his cheeks. However, a sensitive DNA test should be able to detect that the sample is haploid (sperm/egg) rather than diploid (normal cell) $\endgroup$ – CSM Jan 6 at 13:22
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In 2000, DNA tests were portrayed in the media is very reliable. Criticism began to appear, but had not yet entered the public media much (academic publications go back to around 1990).

The safe bet for Joe would be to be out of the city during the duration that the police is taking samples. That might be a couple weeks. I he has something going for him (business trip, ill parent that needs care, etc.) that is not suspicious, it might be his best bet.

It is likely that police will follow-up with people that didn't take the test, but Joe could assume that the published dates are the only important ones.

Following the media and information available to him, I don't think Joe would come to the conclusion that he has a good chance of fooling the test. Evading it seems like a much better idea.

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I'd like to suggest another method of obtaining other mens' DNA that Joe certainly understands and needs not resort to cannibalism / murder / robbing a blood bank. It ensures a man's (or mens') DNA and not a woman's. It's easy to accomplish. It may not fool the actual test, as the lab probably checks cell type under a microscope, and these may be very… wiggly, depending on time between collection and analysis as well the medium. But it sure makes for a good story ;-)

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Chew Plutonium for a few hours.

This will seriously alter the DNA of anything in his mouth.

He will die of radiation poisoning a few days later but JOE is desperate and seems a bit dumb so why not?

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  • $\begingroup$ Where would he get the Plutonium? Even if there was a nuclear power plant nearby, the average small-time criminal wouldn't get far enough to steal some of the stuff. $\endgroup$ – Elmy Jan 9 at 5:37

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