But why don the SWAT outfit if it was supposed to be a murder made to look like a burglary gone wrong? There are much easier ways to conceal your identity than that. A good Ole skin mask and a set of black baggy clothes would disguise his silhouette and cover his face well enough and they are much easier to transport and get rid of than a SWAT uniform. They are also easier to buy anonimously. So why SWAT uniform.
Also, why a murderer waiting for his victim would make so much noise? Breaking glass, hammering on stuff, all in the time when their target can appear at the church, it's risky. And you do not need to destroy random stuff to make it look like a burglary. Open some cabinets and drawers, mąkę a bit of mess and voila. Far less napisy and gives an impression someone was looking for money or valuables.
For me it looks like a job od some very immature emotionally person, that has some elaborate fantasies of power. I think he is an avid gamer, there are games about SWAT, where the player has to go through the rooms in a location, clear them and secure some Irena. Perp's behavior looked just like an emulation of such a game. I think he is a young adult, probably with his own car and he broke into places before. Think weird break ins where nothing of value was taken, but the place was more or less vandalised. I think this time he felt safe, as he got away with the previous break ins, much too safe, because he was so busy roleplaying he did not hear Missy aproaching. She surprised him, maybe even recognised him and in a panic he decided to kill her.