Continuity mistake: There are some major continuity errors in the rescue scene at the end: First, the loader is missing from the side of the grave during several of the shots. Second, the rope changes position. The CSI crew is shown manning the rope, which is running parallel to the ground, ready to pull Stokes out of the grave. (There is a physics problem with this anyway.) The next shot is a close up of Grissom and Brown and the rope is now going up at a severe angle. Brown can barely reach it. (The stuntman can only be pulled out from above, the aforementioned physics problem, and the rope is leading up to the rigging.) Third, immediately after the stuntman is pulled from the grave and right before the explosion, there is no one and nothing near the grave. The loader ends the scene right where it started: on the edge of the grave, bucket up, lights on.
Continuity mistake: When Grissom is on top of the box, talking to Nick, and he tells Nick to put their hands together, you can see that from shot to shot, the alignment of their hands changes. In one shot (from Nick's angle), Grissom's hand is higher than Nick's, as well as Grissom's index finger lines up with Nick's middle finger. In the next shot, their hands line up perfectly. The alignment changes throughout those few shots.
Other mistake: There is no way a body can be pulled out of a grave the way they showed. It would be a pretty tough trick to pull off with a 6', 200lb piece of lumber and virtually impossible with a body. If it was a solid, non-flexible piece of material, pulling on the rope would drag the item until it hit a ledge and then flip it out of the grave. The body is very flexible, especially at the waist. You'd have to pull a body from above, which they end up doing in real life.
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.