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 bullets 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 unarmed guard, Jesus Campos, after unleashing his barrage of fire on the crowd, where 58 people were killed and hundreds were injured.

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 time frame that some of this could’ve been mitigated.”

Campos reported to hotel security dispatchers that he was shot before Paddock opened fire on the crowd, Assistant Sheriff Tom Roberts told The Los Angeles Times. Campos ran down the hall, away from Paddock’s room, after he was shot and may have used both his radio and a hallway phone to call for help, he said.

It wasn’t clear exactly what time Campos called for help or if the hotel had relayed the information about the shooting to police. Las Vegas police did not respond to questions from The Associated Press about whether hotel security or anyone else in the hotel called 911 to report the hallway shooting.

But the sheriff has said that Las Vegas police officers searching the hotel for the gunman during the attack did not learn the guard had been shot until they got off the elevator on the 32nd floor and met him in the hallway.

Nicole Rapp, whose mother was knocked to the ground and trampled by panicked concertgoers as bullets rained from above, said she’s “having a hard time wrapping my head around” why police changed the timeline of the shooting.

“It’s very confusing to me that they are just discovering this a week later,” she said. “How did we not know this before? It’s traumatic for the victims and their families not to be sure of what happened.”