I tend to agree with your thoughts on inexperience and panic.
My biggest question since the beginning has been why the LACK of a firearm? This is Texas, and more people have them than don't.
- Does SP have no access to a firearm, or unable to legally obtain one like a felony conviction?
- Does the SP not have/use guns at all?
- Is SPs home life (kids/spouse) such that they can't go out and buy one without the expense being noticed?
If this was a targeted murder, I would expect that a firearm be used. Since we haven't heard of a firearm I have to assume one of the conditions above most likely applies.
However, overkill combined with burglary tools makes me think that SP was "joyriding" in breaking in and wandering the church in the middle of the night, uniform for the benefit of the cameras - and perhaps to cast doubt on LE - and was surprised, possibly just wanted Missy to stop screaming/running and panicked and overkilled. I hate to get graphic but I bet Missy knew the moment she came face to helmet with SP that something was very very wrong with the situation and tried to book it out of there.
- Maybe SP is anti-law enforcement
- Maybe SP has a new-ish drug addiction to finance. I say "new" because an experienced addict knows how to score easy money with much less effort. New burglar would think they are clever to break into their church
I think the location is targeted, not Missy. SP lives nearby, has friends that attend this church or even attends the church himself.
All my own opinion