We don't know what the PI's think. Sometimes PI's hide and watch, and wait. I'm not ready to take PN off my accomplice list. If DB was responsible for Lisa's death, if there was a death, IMO, PN would help her. They are very close and have been since their mother's death on his 10th birthday.
I wonder why they went to PN's house instead the Irwin's home...or DN's home.
As for him buying the house, I doubt it. He worked at a convenience store, though I'm not sure what he's doing now. For some reason I'm thinking the house belongs to a relative, but I could be way off.