His family found out about the shooting, and their brother's possible involvement, when they were contacted by Las Vegas police early Monday morning.
Paddock's brother, Eric Paddock, who lives in Florida, talked briefly with the media.
"We are completely dumbfounded. We can't understand what happened," said Eric Paddock.
He described the news as being like an asteroid falling on them and that the family has no idea why this happened.
The gunman's niece, Nicole Paddock, posted her sympathies and shock on Facebook. She admitted having only limited contact with her uncle, but echoed the feeling that the motive was unknown.
"I want to express my deepest sympathies to everyone affected by this massacre, I am as shocked and appalled as anyone about this senseless act of violence," she wrote."I cannot speak to what possibly motivates someone to do something like this nor what his specific motivations may have been. ...My family and I are still in shock by this news and my heart goes out to all of those who lost or had loved ones injured in this tragedy. I am at a loss for words."
The family says they're helping the Las Vegas police with the investigation in any way they can.
WHO IS STEPHEN PADDOCK?