How can elemental magic aid forensic in a magical murder?

Question

The ideal murder weapon is probably an icicle, because then you can melt the evidence

Well, it's far from perfect. At least when magic kicks in.

The story is set in this modern world, with elemental magic added in (fire, earth, wind, water). Magic users can manipulate their element (move, change shape, change state) with regard to (not-hard)science.

No manipulating heat for fire user, though.
No manipulating dust for earth user, except if it directly originated from ground.

Magic users are rare. They got their power either from their bloodline, or from a spontaneous mutation. The element is inherited. Though there's no successful record of mixing two elements to a child, there are very, very few that can manipulate two elements at once. It is suspected that they are very rare spontaneous case, or the result of an experiment.

Magic is widely known, though. Magic users are both feared and respected. They can use magic without any effort and without any drawbacks. However, the society has long stabilized since the Witch Hunt, and most magic users (especially within a household) are responsibly using their power. Among the respectable jobs, some choose to work for the police force as a forensic investigator.

I'm mainly interested in how a forensic investigation can be conducted with the aid of elemental magic when the murder is done magically?

For this question, let's use the example in the icicle murder. The icicle may or may not be made by a water user, it is not known yet (although it is made by a water user). It is not important how to identify the murderer, or whether the murder is magical or not.

I'm thinking of a wind-user that can use wind-magic to gently remove dust, or powder used to identify fingerprints, but it seems very trivial. There's no other kind of magic (like divination, teleportation, or such) except elemental magic.

Is enhancing forensic investigation by elemental magic plausible? What are examples of the techniques that can be aided by elemental magic?

Note: It is very different from Magic and the Legal System since it allows divination based magic to help closing the case. Most answers are based on divination school spells, so it's gone very boring reading other answers.

Answer 1

To answer the first question, yes, I believe having a little magic here and there would be useful in an investigation, but its use would be limited.

To be honest, it depends on how you look at it. There’s really two sides to a magical CSI, if you think about it. They’ve got their magic, but they’ve also got their brains. Obviously, magic is their key tool, but them having magic might also have some effects on how they perceive a crime scene. With that in mind, you could have two separate approaches. The second, though, is the more notable.

1.) Uses of Magic in CSI

Beyond a few base operations, there aren’t actually that many uses for the type of elemental magic you described. A few of the ones that do come to mind, though, include:

Earth— Examination and collection of footprints in their original form from dirt/mud, possible ability to analyze dirt/mud found on the crime scene (it’s a real thing—sometimes you can find the region the dirt on Vehicle X’s bumper came from and use that to find out where the vehicle could have been), and excavate makeshift graves left behind by the killer in a whole lot less time than a team of people with shovels could do it.

Water— Not really a whole lot; maybe taking or preserving blood samples, or recording or manipulating the humidity of a crime scene to preserve evidence. Additionally, would be good for freezing certain types of evidence (blood, bones, or anything else organic, pretty much)

Fire— Aside from burn tests in a lab (which could easily be done without magic) and maybe flame control onsite, not a whole lot of direct users for fire magic, since fire is so destructive and thus a hazard to the crime scene.

Air— Probably actually pretty useful when it comes to collecting samples of foreign gasses on site. More mundane stuff might include something like trapping flies off a body in vials with gusts of wind for lab analysis. Very specialized, though, not a whole lot of generalized uses.

2.) Uses of Magic-Related Knowledge in CSI

I think this is the more interesting of the two options. If you assume that a magician with a certain type of elemental magic has studied his or her element to the point that they know it better than most people, then their extra knowledge, while not a direct effect of their magic, could be invaluable. Examples might include a fire elementalist being exceptionally good at arson cases because they know the way fire behaves, allowing them to track down the source of the fire quickly, or an water elementalist who specializes in finding things that criminals have dropped into rivers or oceans because they have a deep understanding of how water flows. I won’t go into too much detail ‘cause it’s not exactly what was asked, but I think the secondary knowledge of the elementalists might be more valuable than their actual abilities when it comes to CSI.

Answer 2

I agree with others that ability to 'interrogate' elements over which one has magical influence would be most beneficial, for example, can water 'remember' being ice?

The Chinese Wu Xing recognises five elements: Earth, Wood, Water, Fire, Metal - they sound far more useful for your purposes.

EDIT: I've abandoned the Chinese Elements Idea, although I still think it good

Manipulation of elements by magic must, though, leave some evidential trace - though it may be difficult to find. Even, according to the OP, fire users cannot manipulate heat (I find it a bit difficult to understand that), so implicitly making ice magically does not involve freezing, only a change of state.

So how easily does a magical icicle melt? And does it melt normally? An icicle melting normally would melt from the outside in, as heat transfers from the environment - but a magical change of state does not seem to involve changing temperature, so the melting process is likely to be different - does the magical change of state just collapse?

The difference between a slow change of state, aka ordinary melting, and sudden change, aka, magical collapse, is likely to produce different forensic evidence. No 'sensing' required.

For example: slow melting produces slow leakage of cold water and some absorbtion, since it will tend to be absorbed as it melts, it will not cover a large area. Sudden melting will create a rush of water, possibly at ambient temperature - this will spread over a wider area. If observed by any means, it is likely to be sudden and dramatic.

Answer 3

Forensic Agents

They mostly use science to try to understand the marks in the body of a victim, little clues in mostly everything that is around a murder, that could help the detective to find the truth. If there is a common occurrence that people use magic to commit crimes or at least in some part of it. Having an expert in this type of manipulations would help in analyze any "trace" left for it.

Most of the cases an agent had to investigate are really standard. It is uncommon to find what you see in a TV show, about a super intelligent assassins that can do anything without people tracking him.

An example: The detective arrives at the location of a hit and run accident, the forensic agents are collecting evidences and taking pictures of the body, taking measurements, looking for possible clues of the type of car involved in the accident.

Most of the investigation and imagination is done for the detective in charge of the case. The forensic agent mostly is an expert in detection, handling and storage of the physical/digital clues of a case.