A maintenance worker has claimed he told hotel dispatchers to call police and report a gunman had opened fire with a rifle inside Mandalay Bay before Stephen Paddock began firing from his suite into a crowd at a nearby country music festival.
The revised timeline has renewed questions about whether better communication might have allowed police to respond more quickly and take out the gunman before he committed the deadliest mass shooting in modern US history.
Worker Stephen Schuck told NBC News that he was checking out a report of a jammed fire door on the 32nd floor of Mandalay Bay when he heard gunshots and a hotel security guard, who had been shot in the leg, peeked out from an alcove and told him to take cover.
'As soon as I started to go to a door to my left the rounds started coming down the hallway,' Mr Schuck said. 'I could feel them pass right behind my head.'
'It was kind of relentless so I called over the radio what was going on. As soon as the shooting stopped we made our way down the hallway and took cover again and then the shooting started again,' Schuck continued.
Police said Monday they believe gunman Stephen Paddock shot a hotel security guard through the door of his suite six minutes before he unleashed a barrage of bullets into the crowd of concertgoers, killing 58 people and injuring hundreds more.
The injured guard used his radio and possibly a hallway phone to also call hotel dispatchers for help.
Gunshots can be heart in the background of the radio call, with the guard telling the dispatcher, 'Call the police, someone's firing a gun up here. Someone's firing a rifle on the 32nd floor down the hallway.'
That account differs dramatically from the one police gave last week when they said Paddock fired through the door of his room and injured the unarmed guard after shooting into the crowd.
The company that owns Mandalay Bay has questioned the new timeline.
'Our officers got there as fast as they possibly could and they did what they were trained to do,' Las Vegas assistant Sheriff Todd Fasulo said.