Good theory!
My first thought about the vest was the person had blood on their shirt and saw/grabbed the vest on the way out of the house as a quick cover up..idk jmo
I think it is a good theory because I noticed in some of those photos is one of those neon little man traffic signs leaning up against the wall along the driveway. The killers may have planned to pull that Amerit truck right up to the driveway and work on the Mosler. I doubt any of the neighbors would give it a second thought. But for whatever reason, they ran out of time to pull all this off.
JMO