A laptop computer recovered from the Las Vegas hotel room where Stephen Paddock launched the deadliest mass shooting in U.S. history was missing its hard drive, depriving investigators of a potential key source of information on why he killed and maimed so many people, ABC News has learned.

Paddock is believed to have removed the hard drive before fatally shooting himself, and the missing device has not yet been recovered, sources told ABC News.

Investigators digging into Paddock’s background also learned he purchased software designed to erase files from a hard drive, but without the hard drive to examine it is impossible to know if he ever used the software, one source said.