Floppy disk among clues leading to BTK capture

Dennis Rader, the former ADT security systems worker alleged to be the BTK killer, was identified in part by "hidden" traces of data on a floppy disk.
Two weeks ago, BTK dropped off a package at Kansas television station KAKE, which included a floppy disk linked to a computer at Rader's church. "They asked me if I had a list of people who had access to our computer and I provided a list of people for them," said the Rev. Michael Clark of Christ Lutheran Church. "Yes, [Rader] was [on that list]."
According to reports, the disk had been used before. Investigators "electronically peeled it back" to reveal older data that had not been erased when the disk was written over with newer information -- a common digital forensics technique. A computer from a local library has reportedly also been seized. Link