Hi,
We haven't done a developer journal on it recently but we have spoken about it a few times, so I can explain some of this for you! :) At the broad level, when a character breaks a law, they leave behind evidence of their crime. Most people will never notice this evidence, and it will fade away in time, but someone with the forensics skill can examine this evidence to gain clues about the crime. That might reveal a trail that can be tracked, sure, but most clues are more about painting a picture of the crime that took place -- about adding knowledge of the crime to your knowledge base so that when you interview other characters with the interrogation skill you can ask them about the details you've learned to maybe learn who might be involved.
For example, you may reveal that thieves' tools had been used to force a lock and take that information to a tinkerer to ask them who might purchase thieves' tools or who might make them. That then points you to someone else, who hopefully points you in the right direction until you have a name for your target.
The type of evidence you find, and the knowledge it reveals depends on your knowledge base and your forensics skill vs. the abilities and actions of the criminal in question used to hide their deeds. You might be the sherlock holmes of Elyria and walk up to a crime scene and immediately discern that you're looking for a 2.3 meter tall assailant with a long stride, which immediately singles out the only Yoru in town. Or you may find a single thread that a tailor identifies as pteroguine hair, which no tailor in town uses, indicating a foreign interloper of some sort, likely from the north. Or you may notice a literal set of foot prints, setting you on a trail that leads you to a potential bolt-hole or a fence or someone else to question.
Forensics is one skill in a suite of tools a detective will want to master that includes interrogation and tracking. Between the three though, it should be possible to do the legwork necessary to find a criminal, but it won't be guaranteed and it won't be automatic. You will have to pound the street yourself, so to speak.
Hope that helps! :) Feel free to ask specific questions if you have them!