Paddock checked into Mandalay Bay a week before Las Vegas massacre, officials say

Almost two weeks after the deadliest mass shooting in U.S. history, the timeline of events is still unclear.
3:33 | 10/14/17

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Transcript for Paddock checked into Mandalay Bay a week before Las Vegas massacre, officials say
We begin with the new timeline from Las Vegas. Authorities coming before the cameras 12 days after the massacre with another timeline. For the first time we are seeing the hotel security guard in the middle. We learn when he was shot. When did the gunman start firing on the crowd and for the first time we are hearing the gunman also trained his weapons on the first responders. ABC's Matt Gutman leading us off from Las Vegas. Reporter: Tonight, the Las Vegas sheriff unveiling that new timeline. Excuse me for my emotion. Reporter: With his voice cracking, he now says he agrees with the timeline put out last night. I am very well aware of the mgm statement provided yesterday. I kbree with their statement. Reporter: 12 days after there have been questions about whether the response could have been quicker. Tonight the Las Vegas sheriff says it was at 9:59 this security officer just 25 years old in this image responds to a door alarm and finds a barricaded door on the 32nd floor add adjacent to the killer's suite. The sheriff said within minute that is security officer is shot by the gunman at approximately 10:05. Mr. Campos received his wounds in proximity to 22:05. He attempted to relay that information via his radio. Reporter: He says it was the same time the gunman fired on the crowd. 22:05 the number provided earlier referenced the majority of fire upon our community. Reporter: Paddock raining hundreds of bullets on the crowd of 22,000 for ten minutes and two minutes after the gunfire ended the sheriff's teams arrived on the 32nd floor at 10:17. 12 minutes after paddock began firing they determined the shooting had stopped. We did not believe we had an active shooter. Reporter: Also tonight, the sheriff's stunning revelation that paddock attempted a more catastrophic attack aiming for those fuel tanks so visible from the air. You could see how far some bullets traveled going over the fairgrounds and hitting the fuel tanks on the other side. The sheriff revealing that his own officers arriving at the scene you see rushing for cover and protecting civilians may have been specifically targeted. One of them Brady cook. Brady sustained a substantial wound to his shoulder. Through his bicep into his chest and out his back. And the reason why I bring this one up -- he asked me if he could go back to work tonight. Matt gut live with us. If sheriff saying the FBI will take a larger role and federal Raul authorities said this money gunmen did act alone. No evidence of affiliations yet. Reporter: The FBI is taking over because of the scale of this investigation. They have hundreds of eyewitnesses to speak to, hundreds of police officers and countless hours of police video. The FBI is focusing on a timeline and motive. They don't know why he did it, only that he acted alone. David. Matt Gutman leading us off. We turn to the health care

This transcript has been automatically generated and may not be 100% accurate.

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