The brother of Las Vegas gunman Stephen Paddock has been arrested on suspicion of possessing child pornography and sexual exploitation of a child.

Bruce Paddock, 58, was taken into custody in North Hollywood, California, for the possession of over 600 images of child pornography and 19 counts of sexual exploitation dating back to January 2014.

The Los Angeles Police Department said the investigation began “after evidence was discovered inside a business” in Sun Valley, California.

Police said, “[Bruce] Paddock had been squatting inside the business and after his eviction, the evidence was discovered”.

Mr Paddock is being held at the Los Angeles Police Department’s Metropolitan Detention Centre. His bail was set at $US60,000 ($A78,000), according to police.

It is unclear whether Mr Paddock has obtained a lawyer.

On October 1, Paddock’s brother, Stephen, carried out the deadliest mass shooting in modern US history, killing 58 people and injuring hundreds of others when he opened fire from the Mandalay Bay hotel in Las Vegas.

Police continue their exhaustive search of clues for a motive.

Police have studied Stephen Paddock’s computer, political affiliations, behaviours and finances, with investigators saying they have combed through 1000 leads and a “voluminous amount of video” footage to no avail.

US authorities have been in contact with the shooter’s Australian girlfriend, Marilou Danley, and have met with Paddock’s other brother, Eric.

Eric told reporters he had no idea his brother would be capable of the mass shooting and could not imagine a motive.

“I don’t know how he could stoop to this low point, hurting someone else. It wasn’t suicide by cop since he killed himself,” he said.

“He killed a bunch of people and then killed himself so he didn’t have to face whatever it was.”

– With agencies