Continuity mistake: Ben joins Judge Carter Addison in his room in the first part of the episode. Addison is on the phone. Before he finally hangs up, he says, "Okay, I'll see you then." Before it cuts away, you can see Dick Van Dyke putting down the smoking pipe that is firmly between his teeth in the following close-up. (00:10:05)
Continuity mistake: Charlene comes back to the office after subpoenaing Piper Laurie. Ben is at his desk writing some notes. However, the pad turns 90° as the camera angles alternate. (00:19:50)
Continuity mistake: When Andy Griffith and Dick Van Dyke shake hands at the club, The Judge is holding his pipe at a different height in the separate shots. (00:24:00)
Continuity mistake: When The Judge is on the stand and Matlock approaches him to start his examination, Andy Griffith's right hand is on/off the railing, depending on the camera angle. (00:39:40)
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.