How do magic forensic works?

Question

Imagine a detective using a special kind of instrument to see the lingering leftover of magic spell at the scene, markings such as spell circle could help to identify type and nature of the spell used and the damage to the surrounding hints the magnitude and strength of magic casted. It would be more efficient if magic is unique to individual much like DNA, however I dislike borrowing the concept of chromosome because it is too complicated and redundant.

Question: how can I make each spell unique to their caster but still base on a single magic system? For example the detective and use the finding to trace a certain individual but I don't want to duplicate the DNA to use for magic it's redundant and messy.

Answer 1

Perhaps the best approach to this is to borrow an idea already present in forensic science: signatures. Signatures are unconscious attributes of an act: e.g., a left-handed person will tend to cut from right to left, while a right-handed person will tend to cut from left to right; a person with a particular obsession will tend to recreate the same act over and over, while someone less obsessed will show more variation. An investigator could then look at (say): the type of magic invoked, the particular tools used, idiosyncrasies (like using spells from an uncommon source), variations (like using phrasing peculiar to a particular region). Thus, a detective might notice that a spell uses the magical alphabet of a certain region, the magical tools of a certain sect, and language that refers to the thinking of a particular magical source, and narrow down the caster to those who have been exposed to all of those influences.

Detective work is just the application of logic: who wanted to do this, who understood what to do, and who had the skills necessary: motive, means, and opportunity. Magic is just a different source of means and opportunity, and once one understands what had to have been done, one can look for those able to have done it.

Answer 2

Don't get hung up on "DNA". There are all sorts of ways of uniquely identifying individuals; fingerprints, retinal patterns, voice prints, auras (if you believe in them, or if they exist in your setting), even things like how they walk (gait analysis). It no particular stretch for magic to be the same. Sure, many magic users might use the exact same spell, but there's no reason why the use of that spell shouldn't also leave a distinct magical impression.