Diary of a Perfect Murder - S1-E1
Character mistake: Prosecutor "Death Row" Hawkins finishes speaking with prospective jury member Mr. Cooper and tags in The Defense attorney, saying, "Mr. Matlock, your witness." Naturally, Cooper is not a witness of anything; they are selecting the jury.
Answer: I did not see this episode, but YES. Both prosecution and defense lawyers use investigators to search for and uncover evidence that is legally admissible.