Continuity mistake: Season 10, episode 3 "Working Stiffs": The picture of the employees holding a sign at work with the X's through them at Paulie's house changes between two completely different photos when far away vs. up close.
Other mistake: Season 10, episode 4 "Coup de Grace": When Nick is doing the phenolphthalein test on the q-tip, it turns pink immediately and starts to overflow pink coloring all the way down the side of the stick, which is not how that test works. Normally it takes a few seconds and only turns color around where the blood is.
Continuity mistake: When Brass calls Dr. Ray and gets his voicemail instead, Brass raises the phone to his ear twice. (00:02:00)
Continuity mistake: When Nick asks Dr. Ray what he's doing out on the Strip instead of at their crime scene, and Ray shows him the photograph of Madeline Briggs, his hand moves from the top of the photo to the bottom in consecutive shots. (00:03:20)
Continuity mistake: When Hodges shows Dr. Ray and Nick the information from Dede Chase's cell phone, Ray's arms change position between shots from the tabletop in front of him to crossed across his chest. (00:08:55)
Continuity mistake: Near the start, when Ray is showing the photograph of Madeline with the security guard to passersby asking if they've seen her and also when he shows it to Nick, we can see the photo Ray is holding out in the wide shots, but in the two closeups of the photograph it's actually a different photo. Then later, when Ray shows the photo to Madeline's mother it's the same as the one from the closeup earlier.
Other mistake: In the first scene when we see Dr Langston from behind as he's watching people passing by he's wearing glasses but when we see his face he's not wearing any. (00:00:15)
Revealing mistake: When Nick is in the shed in the desert, sunlight is coming in through hundreds of holes in the walls and roof. Since the sun is in one spot, all beams of light should be in the general same direction. In this scene they come from at least 5 different directions, with some originating from a light source very close to the outer wall (causing beams in a radial pattern).
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.