The revised timeline given by investigators for the Las Vegas massacre raises questions about whether better communication might have allowed police to respond more quickly and take out the gunman before he could kill and wound so many people.
On Monday, Sheriff Joe Lombardo said Stephen Paddock shot and wounded a Mandalay Bay hotel security guard outside his door and sprayed 200 shots down the hall six minutes before he opened fire Oct. 1 from his high-rise suite on a crowd at a country music festival below.
That was a different account from the one police gave last week: that Paddock shot the guard, Jesus Campos, after unleashing his barrage of bullets on the crowd. He killed 58 people and injured hundreds more.
The sheriff had previously hailed Campos as a "hero" whose arrival in the hallway may have led Paddock to stop firing. But on Monday, Lombardo said he didn't know what prompted Paddock to end the gunfire and take his own life.
"This changes everything," said Joseph Giacalone, a professor at John Jay College of Criminal Justice and a former New York City police sergeant. "There absolutely was an opportunity in that timeframe that some of this could've been mitigated."
Giacalone added: "By engaging the shooter ahead of time during this event, it could've saved a lot of heartache."
Police have released few details about the new timeline and did not respond to questions from The Associated Press, including whether anyone called 911 to report the hallway shooting.
"Our officers got there as fast as they possibly could and they did what they were trained to do," Assistant Sheriff Todd Fasulo said.
Fasulo explained the change in the timeline by saying that dozens of investigators have been using different sources of information — including surveillance video, computers, police body cameras, cellphones and interviews — and that not all clocks are in sync.
Last week, police said Paddock had shot at concertgoers for 10 minutes and stopped firing around 10:15 p.m. The first officers arrived on the 32nd floor at 10:17 p.m. and encountered the wounded guard at the elevator bank about a minute later, police said.
The security guard had been responding to a door alarm on the floor when he heard drilling that he found odd, Undersheriff Kevin McMahill told KNPR on Tuesday. That was when Paddock fired hundreds of rounds at the guard and a maintenance man, McMahill said.
Paddock had power tools and was trying to drill a hole in a wall, perhaps to mount another of the security cameras he set up around him, or to point a rifle through, but he never completed the work, Lombardo said. He also drilled holes and bolted a metal bar to try to prevent the opening of an emergency exit stairwell door near his room.
Las Vegas police officers had been searching the hotel for the gunman and did not learn the guard had been shot until they met him in the hallway after getting off the elevator, the sheriff has said.
"The police officers themselves could've engaged Paddock and at least taken the gunfire instead of him shooting out at the festival," Giacalone said.
Associated Press writers Ken Ritter and Sally Ho in Las Vegas contributed to this report.