Friends, let us imagine (purely for argument's sake) that neither Mr. Truly nor Mr. Shelley knew of the plot beforehand. In all innocence, they hired a team of carpenters to come in for a big floor-laying project.
The assassination happens. Once it is established that everyone in the
internal floor-laying crew left the sixth floor for their break, Mr. Truly and Mr. Shelley realise in horror who must have carried out the assassination.
Do they
a) tell the authorities all about this crew?
b) keep schtum (out of personal fear of reprisal and of being arrested for complicity), and get the internal crew to pretend they and they alone had been doing the floor-laying?
And once Mr. Oswald is singled out as the prime suspect, do they
i) defend their man, even at the risk of drawing heat on themselves?
ii) let him be fed to the wolves by doing all they can to help the authorities' ridiculous LN narrative?