Transcript for The timeline of the Las Vegas massacre remains unclear almost 2 weeks later
developing headline from las Vegas. Tonight, the hotel now revealing its own timeline, involving that hero security officer who was shot and who then called for hel help, and the massacre. ABC's Matt Gutman back in las Vegas. Reporter: Tonight, the owners of the mandalay bay out with a new timeline. The company disputing what police have said and insists there was no six-minute gap between the time that Stephen paddock shot a security guard in the hallway and the moments he opened fire on the 22,000 concert-goers down below. In a just released statement, the hotel chain says "The rampage began at most 40 seconds after the security guard reported he'd been shot." The implication? By the time hotel security was notified about a gunman, the massive attack was already under way. Campos wasn't the only one who called security. A maintenance man on the same floor did, as well. Call the police. Someone's fired a gun up here. Someone's fired a rifle on the 32nd floor down the hall way. Reporter: The hotel tonight saying Las Vegas police officers and hotel security were already in the building and were dispatched immediately to the 32nd floor. And Matt with us live. Matt, this is a different timeline from what the police have presented. Reporter: It's wildly different. Now, the Las Vegas police department is going to roll out its new timeline tomorrow, but what's so shocking is that 12 days after the worst mass shooting in U.S. History, the police here still can't tell us exactly what happened and when. David? All right, Matt Gutman with us tonight. Matt, thank you.
This transcript has been automatically generated and may not be 100% accurate.