The timeline for the worst mass shooting in modern U.S. history initially established by Las Vegas Metro Police and the FBI has changed.

Originally it was believed that the arrival of Mandalay Bay security guard Jesus Campos had stopped Stephen Paddock from firing into the Route 91 Harvest Festival on Oct. 1, when Campos discovered Paddock in his room on the 32nd floor.

On Monday, Clark County Sheriff Joe Lombardo announced that the timeline was incorrect and that Campos was actually shot by Paddock prior to the mass shooting, the Las Vegas Sun reports.

“Mr. Campos was encountered by the suspect prior to his shooting to the outside world,” Lombardo said. “He immediately, upon being injured, notified security of his situation. In close proximity of Mr. Campos being shot there was also a maintenance worker on the 32nd floor. Mr. Campos prevented him from receiving any injuries.”

At 9:59 p.m. Paddock fired “well over 200 rounds” into the hallway, striking Campos in the leg, six minutes before he fired into the music festival crowd below.