Theories

Warning This Section Does Contain Spoilers

For some reason Penny did not tell the full story, or she may not have remembered the exact order of events due to trauma and PTSD surrounding the incident of losing her husband and son. She admits to hearing the shot that killed her son, although she didn't tell police this. She also admits to us that she struggled with her husband over the gun to keep him from killing himself, although a shot was fired anyways and he was killed. The evidence seems to back up her version of events. It seems that she could be innocent. It appears that the entry wound looks like it could very easily have been fired by Kenny's own hand and would be unlikely that he would sit there and just let her fire a bullet into his head without putting up a fight, but there were no defensive wounds found on the body. He would have had to have been sitting down for her to be able to walk up and murder him. In her psych eval interview she does say he was sitting at his desk, but that still would mean she would have had to walk up to him without him knowing it, after killing the boy, which is unlikely.