I don't really have theory. Partridge and Bertram are my favorites.
Partridge lost a little bit points in season finale even I agree to the cues introduced here.
Like he denies if RJ did the murder, smiley face next to him saying look at me, it's me etc.
But I believe since Lorelei came back to picture that everything have been setup by her and PJ.
Season finale was all about PJ confirming his views.
He was really demanding when asking Partridge's opinion. It felt like PJ already knows what is the truth in this case and he simply wants to see the reaction and answers of Partridge. I think this kill was not RJ like Partridge insisted.
Lorelei is alive and she and PJ did the video recording.
Throughout the season finale for some reason PJ is constantly setting ideas In Lisbon's head like this 'happy memory'. Most likely Lisbon is blackmailed somehow by RJ. When Lisbon is watching the Lorelei video, PJ is paying heavy attention to her reactions on each picture. In the end Lisbon turns her head to left - Bertram.
Other option is that Lisbon hurt her hand while giving hard time to Lorelei; right hand -Lorelei left hand and left cheek. But I don't like this option as it is more logical with setup of PJ and Lorelei.