I'm not sure that's why we know nothing about it. Ashley Babbit's assassination may have been planned ahead of time. She may have been targeted because she knew of the FBI's plans and they needed to shut her up.
You’re making it way too complicated. Simpliest explanation that fits all the known points is best. (Until we know more then we change the explanation!) It is “Capital Hill LEO who panicked ! Aside: An easily panicked LEO is not someone you want with a firearm. (or who wanted to impress his boss - Pelosi .. maybe at Pelosi’s command - far far less likely!)”.
Why so far we know nothing is explained perfectly with the fewest extra steps by the previous poster.