Previously I had said that I didn't think perp had left any of this behind, and had not seen anything to indicate that to be the case.
However, I have since discovered that was not really accurate, as to reflecting what has been revealed to us. Sorry about that, Dedee!
In a PC by LE on the Friday following the murder, we were told "...there were some various tools found around the crime scene that we're analyzing."
.... But that was all they really said. What tools? Brought by the perp, or items from the church premises? Tools seen in the video? Are all items seen in the video accounted for? Are any of them? Tools used in the murder? LE probably knows all of that, but they didn't answer any of that. Nevertheless, they did find "some various tools" of some sort.
In addition, early on they mentioned they had brought in outside agencies, and ATF was one of them (as was the FBI). When we didn't know the death was by gunshot, we speculated as to why they were there. But it's easier to understand now. And if there's any question about how the FBI would have known a gun was the weapon, they were here and involved quite early.
Regarding finding a firearm, I also found that in a later interview (about 3 years later, I think), they mentioned that they did find one firearm; but then added that it was found in MB's vehicle and was not used in the killing.