For anyone asking what forensic linguistics is or what forensic linguists do, you should watch Dr. John Olsson's YouTube video. His video documents the types of comparisons and critical analysis necessary to work with forensic linguistic investigations of language use.
Watching the video will give you a sense of what types of information you can get from language, the types of conclusions you can draw about language use, and how critical analyses of language can help in investigations.
You may have noticed that Dr. Olsson's conclusion was that Chapman "could not be excluded from the authorship of the later texts sent from the teenager's phone." On the surface, that may sound like a vague conclusion, yet it was important to the case. Why do you think such a conclusion was important? Furthermore, why do you think it would not be possible for Dr. Olsson's conclusion to be that Chapman was definitely the author of the text message?
If this video sparks interest for you, you might want to think about taking ENG 438: Forensic Linguistics in the fall.