Simple enough to verify.
Lets go to the video.
What do you mean - what video?
most jails have system to record your cell checks and counts Could be as simple as a slip of paper at the end of the tier or hall with your initials and the time on it.
So if you sign you checked at 3:15 am and the corner says the guy died 12-1 AM you’re up shit creek if they find the body at 4:15.