He went with the police to take Rosa's statement. Rosa did not know much about Bruce's situation at all, but she did give one clue, and that was that Bruce would often call a man named Logan behind her back.
Back then she was still a bit wary of Bruce, so she would often secretly listen to his conversations with Logan. Back then she had wondered if Bruce was seeing other women outside. So while he was in the shower, Rosa had secretly looked through his phone and recorded Logan's phone number down.
The police asked Rosa to give them the phone number that she had recorded. With the number, John found out that his full name was Logan Wheeler.
After some investigation, John found that Logan owned quite a few shops. In order to exert his power, he had quite a few underlings under him. Bruce had indeed worked for him before.
