The FBI and Los Angeles Police Department used a joint task force to carry out the arrest.
Bruce Paddock's arrest was confirmed by a law enforcement official briefed on the investigation but not authorized to discuss it publicly. He is charged with possessing more than 600 images of child pornography, as well as 19 counts sexual exploitation of a child.
Almost a month after the deadly shooting, however, Las Vegas and federal authorities have struggled to come up with a motive for the deadly shooting. The attack left 58 people died and more than 500 others injured.
An attorney who represented Bruce Paddock in past criminal matters told NBC News that he is no longer representing him and declined comment.
Classified JFK assassination files will become public, Trump announces in a tweet
The President, no stranger to conspiracy theories himeslf, may also have a personal interest in some of the released documents. Experts say that they're not expecting any bombshell revelations in the documents.
According to ABC News, Paddock is thought to have removed the hard drive from the laptop before fatally shooting himself following the massacre. The official says the child porn case predates the shooting.
Investigators, however, were unable to locate Paddock because he was homeless.
His older brother, Stephen Paddock, was behind the deadliest mass shooting in U.S. history when he began to fire on a concert crowd from the 32-floor of the Mandalay Bay Hotel in Las Vegas.
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 October 1.