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.