Questions - spoilers

If Katrina didn't kill the first guy, how insanely coincidental is it that the two pieces of art that she mentions possibly having touched were touched by the killer?
Kyle had been showing his art objects to Trina in the afternoon (the mask and the hatchet) so it's probably they were still at the table when Matt got there to kill him. In Matt's mind Kyle was the one who corrupted Trina, so he wanted the killing to the as painful as possible. The hatchet was lying there, he used it. Matt later covered his face with the mask probably to mock him. Kyle was known for collecting masks, so Matt turned him into one of his "art collections".

When a fingerprint ties Katrina to the crime scene, what on earth makes Corelli ask the neighbor if he had ever seen her at the "sex house" rather than simply suspecting they might have got the motive wrong if she were the killer? Based on the info they had, wasn't it highly unlikely that she would have been there, and if the neighbor hadn't seen her there, it would in no way have cleared her.
Corelli was still very much in love with Trina, so he wanted to make sure she was really involved or the fingerprints were just a coincidence, due to the fact she spent the afternoon with Kyle the day he died.

In the break-in scene at the Gavins' house, there's a guy at one point looking through legal files. It was so dark, I couldn't tell if it was supposed to be one of the cops or if the governor's aide had been there and managed to get away without anyone so much as seeing him.
It was the cop who was also the governor's aide, looking for pictures or anything that could relate the governor to Kyle Medford, Trina or Patrice Jacinto. It was revealed Trina was Jade, she had sex with the governor in Kyle's house and they thought she was involved in the blackmail scheme.