Am I missing something here but when Tim O'Connor is tape recording the museum inventory, why isn't the gunshot picked up on the tape recording?

I haven't seen it in a while, but wasn't he pressing the REC button while he spoke and then stopping recording while he looked at the items? I thought that's how he was doing it as opposed to one continual recording.

If not, I guess that's a slipup.

I always wondered about this, too. I haven't seen it in awhile, but I think he was recording and in the middle of speaking when the gun was fired. So even if the gunshot was not heard, Columbo might have noticed it was odd that Tim didn't finish his sentence at that point in the recording. But maybe it happened the way Pete suggested which would be a good explanation. I don't remember.