If you are going for PhD you need to have 3 letters of recommendation from academics. I would advise not to get one from your prosecutor friend.
If you're interested in biosocial, you're gonna want to make sure that you are applying to programs that have people doing this type of work. My understanding is that it's a small subfield that is very separate from the rest of the field. I don't know for sure, but I'm assuming a place like Penn State that has a combined soc/crim program does not have people doing research on biosocial crim. It is important you check, because if you're not a good fit with the program you won't get accepted no matter how qualified you are.