The demo is NOT like a movie its information that the engine uses to render a recorded sequence of the game. ALL DEMOS are the same ( on all clients, server *check EX) and there not the most effective way in catching hackers as hacks don't show up.
EX: player Jimmys demo is the same as player Johns demo (only length may vary) so its best to just runt hltv and record all maps/moments ( if a demo is what you wana have 4 catching hackers )