I tend to believe that Missy was targeted, however the more I think about it with the gun vs. hammer discussion I wonder.
If I was going to target someone that church, that morning was the perfect scenario. I wouldn't use a hammer or knife. I'd definitely use a gun. Rainy morning. Before 0500. The church itself would seem an unlikely place to expect to assault or attempt to kill a person. The building is almost isolated as the gun store is about a 1/2 mile away and residential houses almost that far away with some trees between them and houses. I originally thought a .22 auto with a homemade sound suppressor would be ideal. (No, it's not all that farfetched. Go on YouTube and search for how to make a sound suppressor or silencer for a .22. You can make one with one inch PVC pipe or metal conduit pipe and some items you can purchase at a hardware store.) Then I thought there is too much of a chance to lose one of the ejected casings, so a revolver would be best. No ejected casings. With many revolvers I could use a .22 short hollowpoint as that would make less noise. So I'm inside a building with rain coming down - both help muffle the sounds. I have a good distance between the church and occupied dwellings. If someone else pulls up, chances are they might still be inside their vehicle rolled up and possibly the radio or CD player going. I don't believe anyone would notice the sound of a .22. I wouldn't need a sound suppressor and it wouldn't get in the way of my sights. Two shots, three at the most and I would continue out the back of the church and drive off. Toss the gun in a river or lake. Toss the gloves (gunshot residue). If I'm far enough away from my victim I don't need to be concerned with blood on my clothes. And I'm not the best shot with a handgun.
Using a hammer or a knife requires the killer to up close and personal. Many blunt force murders are the product of a heated discussion or altercation. To use a hammer or knife in a planned assault requires confidence in one's own abilities and cold blooded motivation to go through with it. That is the type of confidence that comes from the kind of training that the Army, Marines or Coast Guard provides. (Maybe police training as well.)
That said, it is not impossible for someone with no training to plan to assault someone up close with a knife or blunt instrument. Happens often enough to not rule it out. And, of course, I'm shooting holes (no pun intended) in my theory that this was a premeditated murder, but rather a robbery/vandalism that went bad. And, too, a person below the age of 21 might not have access to a gun and ammo - vandalism by someone in their late teens?
Just pondering how I would do it. Others might have a different approach.