I was watching this show on TV, and it telled how this guy wrote in his computer, somewhat of a diary, and deleted all of the info. The cops later came by to check it out, and with some software, and computer knowledge, they got parts of the information back, how did they do this? They said how when you delete a file (FULL DELETION), it deletes most of it, but the information is still there, somewhere....They sxplained it like each new piece of information is like a piece of paper being stacked over each other...

How did they recover the info?