Throughout the investigation, the prevailing theory was that the bomber was a former Con Edison employee with a grudge against the company. Con Edison employment records were reviewed, but there were hundreds of other leads, tips and crank letters to be followed up on. Detectives ranged far and wide, checking lawsuit records, mental hospital admissions, vocational schools where bomb parts might be made. Citizens turned in neighbors who behaved oddly, and co-workers who seemed to know too much about bombs. A new group, the Bomb Investigation Unit, was formed to work on nothing but bomber leads.