Common sense tells you that nobody would leave a traceable weapon. They would leave another weapon. Also, the officer had to know that a security sweep was coming and the weapon would be discovered. This was not done on purpose.
You sound like you know more about the process than I do. I will take your word for it being an accident. I guess I am starting to sound like a paranoid DUmmy. Sorry.
Unless they're tricky --
Leave a gun openly there,
at one location,
to draw attention
away from some other spot
where one's really hid . . .
A "high profile" hit
probably would include lots
of indirection.