Las Vegas massacre gunman fired over 1,100 rounds, sheriff says

LAS VEGAS -- The top lawman in Las Vegas says the gunman who killed dozens of people at a concert last month fired more than 1,100 rounds. 

The newly released estimate from Sheriff Joe Lombardo offers more detail about the deadliest mass shooting in modern U.S. history

Lombardo tells the Las Vegas Review-Journal he was aware of the previously unreported figure because his department's forensics lab is working with the FBI to process all ballistics evidence. 

Stephen Paddock killed 58 people and injured hundreds more on Oct. 1 after he shattered windows of his suite on the 32nd floor of the Mandalay Bay hotel-casino and unleashed withering gunfire at the music festival below before killing himself. 

Authorities have said they have not determined Paddock's motive or why he stopped shooting. Lombardo says authorities found about 4,000 unused rounds in the suite.

He said he is frustrated by the lack of progress in determining a motive. Lombardo said police continue to interview Paddock's girlfriend, Marilou Danley, most recently on Monday.