Built to Kill (Part 1) - S7-E1
Revealing mistake: During Katherine's visit with Dr. Robbins, they are overlooking Suicide Guys' body, discussing his autopsy. Just as the doc's hand touches the corpse's mouth, the corpse's lower lip twitches slightly.
Built to Kill (Part 1) - S7-E1
Revealing mistake: When Sarah visits Dr. Robbins to get an update on Suicide Guy, who is being autopsied, the camera moves to the right and you can see Suicide Guy breathe twice, even though he's supposed to be dead.
Answer: He doesn't have the authority to arrest him - when anyone is arrested in the show, a police officer does it. Also he tells Ty that he is going to be submitting his case findings to Ty's insurance company, who would no doubt contact the IRS, who then would have him arrested for fraud etc.