Colonel Aaron Raymond appears in The Silver Briefcase. He was the killer of his wife, Nicole Raymond, eight months prior to the start of the episode.
When Colonel Raymond approached Jane and Lisbon, Jane noticed something was off about his demeanor. He suspected that he was the killer of his wife, and secretly reopened the case.
It was revealed that Colonel Raymond was having an affair with Denise Sparks. Nicole and Aaron were going to get a divorce and she threatened to take the house and everything else, plus drag her husband's and Denise's reputation through the mud. So, they jointly planned Nicole's murder.
Colonel Aaron Raymond turned up the thermostat to make the house really hot. It was never confirmed as who actually stabbed Nicole as during the confession they both accused each other. Denise swapped clothes to make herself look like Nicole and he sped through a stop light to establish an alibi and abandoned the car in a high risk neighborhood hoping it was get stolen to frame the car thief. It worked and Zach Jefferson was framed for the crime.