Santa Claus - S1-E12
Visible crew/equipment: When Mark Harris shows Matlock into his office, the actors' T-marks can be seen on the floor under the chair.
Factual error: This takes place in Atlanta, but in the scene where Tyler pulls up to Matlock and The Professor on the bench, there are California-style palm trees visible in the background. (00:18:35)
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.