When Jack is chasing Hewitt on the rooftop, Hewitt climbs onto a raised level of the roof, then pulls up the ladder to try to keep Jack from catching him. We see Hewitt drop the ladder at the top of the wall, with a portion of the ladder extending over the edge. Jack then climbs a pipe which is attached to the wall, just to the right of where the ladder was placed. When Jack reaches the top, the ladder is gone.
During the rooftop chase, the sky over Downtown L.A. suddenly turns from sunny to overcast with a threat of rain in a matter of seconds.
When Jack first sets foot on the roof, he is looking at the "rising" sun in the direction of the Downtown L.A. skyline, but the bridge in the background is the 6th Street Bridge, which spans the Los Angeles River, east of downtown. Los Angeles' City Hall can also be seen to the right of the Downtown L.A. skyline. Jack is looking at a sunset at 6:05am.
One of David Palmer's staffers 'mistakenly' refers to him as 'Mr. President' after he is removed by the Cabinet. In actual fact, all Presidents continue to be referred to by this title even after they leave office.