A laptop found in Las Vegas mass killer Stephen Paddock’s hotel room was missing its hard drive – depriving officials of possible clues on why he unleashed his attack, ABC News reports.

The madman is believed to have removed the hard drive before he committed suicide, sources told the network.

Paddock also bought software designed to erase computer files, but because the hard drive is missing, investigators can’t determine if he had used the software, a source told ABC.

Authorities have been struggling to find out why the retired accountant killed 58 people and wounded hundreds of others when he targeted the Route 91 Harvest Festival from his perch at the Mandalay Bay hotel on Oct. 1.

Paddock — who left no writings or other evidence about his planned massacre — is not the first mass killer to destroy or hide digital clues, ABC News reported.

In 2007, Virginia Tech killer Cho Seung Hui removed the hard drive of his computer and got rid of his cell phone shortly before slaughtering 32 people.

Investigators even searched a pond for the missing items, but they were never recovered.

The 2008, Steven Kazmierczak, who murdered five students at an Illinois college before killing himself, removed the SIM card from his phone and the hard drive from his laptop. Neither was found.

And in 2012, Adam Lanza, who killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn., had removed the hard drive from his computer and destroyed it.

On Wednesday, Paddock’s brother, Bruce, was arrested in North Hollywood, Calif., on child-porn charges.