The Las Vegas Police Department announced the security guard who was shot by Las Vegas shooter Stephen Paddock was shot prior to the mass shooting began, although previously officials believed he had been shot after the massacre.

Clark County Sheriff Joe Lombardo said Monday in a press conference they previously believed Mandalay Bay security guard Jesus Campos had halted the assault by distracting Paddock from the concert, but they learned Campos was actually shot in the leg minutes before the massacre as he was responding to an open door alert concerning another guest.

Police officers who responded to the shooting did not know Campos had been shot "until they met him in the hallway after exiting the elevator," according to Lombardo.

Officials said they do not know what stopped Paddock from shooting upon concertgoers.

Paddock opened fire from the 32nd floor of the Mandalay Bay hotel Sunday night upon concertgoers at the Route 91 Harvest country music festival.

Paddock was found dead in his hotel room by law enforcement after the shooting.