You started well enough with a tentative speculation ("one possibility is that he heard a sound related to Baker and Truly's running around on the roof, and subsequent descent using the east elevator. Was it the slamming of the door to the roof?") but now you magically convert it into a confident statement of fact ("Anyway, a door or hatch or trapdoor slammed shut").
Re "possibility" here i was quoting i think pat speer or someone else quoting pat speer.
Yes & of course my own confident statement should have had an "i reckon that" in there somewhere. This must be the first time i have ever left out an "i reckon" & i got bitten.
But i am pretty sure. We have Dougherty. And Price. And a cop (whose name i can't remember) on the opposite rooftop (i think he said 4 minutes after the shots).
And no-one seemed to hear at ground level.
And the pigeons hadn't yet returned. Mightbe they never did return.
And on a different subject i have edited my older postings to erase mention of a power outage, until i see proof of an outage.