The Security Officer Isn't the Man in the Video

The security guard assigned to that location had been committing fraud for multiple weeks. He would use his phone to self-report into locations that he actually wasn't at. Aaron is just on level five before he gets to the big boss, because he still has to find out if the security guard isn't the man in the video. Why did he quit his job so abruptly after Stephen's murder? I've got a mystery.