Legal disclaimer: The following is just my opinion and for entertainment purposes:
I've been involved with LE for over 17 years with the last 9 specifically in burglary and violent crimes. I've seen hundreds of videos where a perp has broken into a building (commercial, school, church, etc) with some type of disguise. They've worn everything from ninja outfits, tactical gear to mascot uniforms. I seen the exact type of nonchalant, slow and easy walk that the SP in the video is showing. In my opinion the SP broke into the church expecting to get something of value. Most church break-ins occur on Sunday and Wednesday nights. During the process of burglarizing this church an interaction occurred between the SP and MB which led to MB's death.
This isn't a staged burglary to cover up a pre-meditated murder. I know a lot of people are stuck on the fact that the SP didn't take the wedding ring. It's because the SP was in a frantic state after the altercation and wanted to get out quick. If this had been a pre-meditated murder the last thing a perp would do is be caught on camera and would've certainly chosen a much easier path. The SP also knows that they are on camera because they looked right at the camera. Simply put, the SP didn't go to the church with the intention to commit murder.
Of course, this is all just my opinion based on years of experience. As mentioned previously, I've seen the behavior the SP displays many, many times in burglary videos. The SP is very comfortable being in a building that they burglarized and I'm very sure this person has been doing this for a long time.