He Felt Betrayed
It was Caleb, one of his trusted workers, sneaking into Joe’s room to find evidence against him and trying to tamper with the evidence he had against his suspects to prove his innocence. The company that he recently ordered new products from was introduced by Caleb; definitely, he had a connection with the main culprits. He was certain he wasn’t involved in the killing, but he was used as a tool to get access to him. Which also makes him a culprit.