The Affair - S1-E4
Revealing mistake: The attempt on Rodriguez's life is quite phony looking; leaving aside the trope of a person who wants to avoid being murdered by a car by trying to outrun it instead of getting out of the way (the first semi-POV of the car does a terrible job at that, since the car looks much closer to The Victim and slower than it should be, and wide room for Rodriguez to escape sideways), the impact does not happen and the stuntman jumps into a pile of garbage without anything remotely close to connecting. (00:32:00)
Revealing mistake: Ben Matlock is hosting a pre-wedding party for his goddaughter. Several cars are parked on both sides of the street in front of Ben's house. Each time the front door is opened, The View seen from inside the house looking out is the same matte painting used in every episode. It shows a house and trees but no cars.
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.