A laptop recovered from Las Vegas shooter Stephen Paddock's hotel room is reportedly missing a hard drive, leaving investigators without what could be vital clues in solving remaining mysteries into the deadliest mass shooting in modern American history.

According to ABC News, Paddock is thought to have removed the hard drive from the laptop before fatally shooting himself following the massacre.

Paddock is also believed to have purchased software that would have permanently deleted files from his computer.

Investigators are still struggling to explain why Paddock opened fire on concertgoers at the Route 91 country music festival on Oct. 1. No clear motive has been presented to explain the shooting.

On Tuesday, Paddock's brother was arrested for possession of child pornography in North Hollywood, California.