And Then There Were None - S2-E9
Factual error: Ballistics expert Bobby Dawson mispronounces the word "Koch" in the term "Heckler and Koch". He pronounces it "kotch" instead of the correct, "koch" (rhyming with lock0. A ballistics expert would know the correct way.
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.