Police investigating the Las Vegas shooting have updated their timeline of the events leading up to the massacre that unfolded on October 1.

Investigators in Las Vegas now believe a security guard who was the first to encounter gunman Stephen Paddock did so at 9:59 p.m. local time — six minutes before Paddock began firing on the crowd of 22,000 concertgoers at the Route 91 country music festival, killing 58 people and injuring hundreds more.

The security guard, Jesus Campos, was shot in the leg by some of the more than 200 rounds that Paddock fired into the hallway outside of his 32nd-floor suite at the Mandalay Bay Resort & Casino. “Immediately upon being injured, he notified security,” Sheriff Joseph Lombardo said of the hotel guard at a Monday evening briefing.