Deliberate mistake: In the episode where Mary-Alice Young's house is open for buyer's inspection, the phone number on the "For Sale" sign has been digitally blurred.
Deliberate mistake: When Susan falls through the floorboards of Mike's house she uses the nearby towel to try and get the dog Bongo to help her. If you watch at the different angles the position of the dog keeps changing. When it shows Susan from behind the dog is almost right next to her face and stepping on the towel. In the shots from in front of Susan the dog is nowhere near the towel or even in the shot. This mistake looks more deliberate as the front on shots of Susan, the dog would likely have blocked her face from the camera.
Answer: He was investigating the lead not the case.