Other mistake: When Brass is asking if a witness or someone they are speaking with knows the victim, you can see the victim's name on the bottom of the crime scene photo before brass is supposed to know the identity of the victim.
Continuity mistake: In the scene where Riley Adams takes a victim's wallet from David Phillips, she takes the wallet with her left hand with no glove on. Next shot Riley has gloves on both hands.
Factual error: When Nick picks up the contact lens from the PI's body, you can tell from the way it bends while he is holding it with the forceps that it is soft and pliable, as if it had just come out of the eye. However, after 6-12 hours outside of an eye or a contact case (the amount of time David says the PI has been dead), a soft contact will dry out and become wrinkled and hard.
19 Down (1) - S9-E9
Factual error: Season 9, Episode 9 - 19, "Down": Towards the end of the episode they are searching along railroad tracks. A MetroLink train passes by. MetroLink serves the greater Los Angeles area, but does not serve Las Vegas.
Disarmed and Dangerous - S9-E12
Plot hole: Series 9 episode 12: "Agent Hartford" had no fingerprints: the FBI "removed" them. But when they find the street piece that Vinny had, they dust it and say that Hartford's prints were all over it. This might be OK, if he were a real agent on the books (but they never heard of him at Quantico), or if he were a real criminal - but in that case, they would have sussed it all out earlier.
Plot hole: Episode 9-18, "Turn, Turn Turn": Greg states that the dead motel manager crawled up into the ceiling the same way that he did, and you see Nick open the access panel in the ceiling. The manager couldn't have closed the ceiling panel after him and no one was managing the hotel in the week he was missing. The panel should have been open when Nick came into the room. The new manager stated he didn't know if there was a panel in that room, since he just got there.
Factual error: At the time where they are looking into the moon and the time, they misstate the time the moon rose in 1997 and they state that the moon was waning, when it actually waxed in the middle of June in 1997. (00:33:00)
Continuity mistake: Season 9, episode 3 "Art Imitates Life": When J. Skaggs is being interrogated by Brass he has his hands on his lap. In the next shot they are both on the table.
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.