New timeline raises new questions about law enforcement response to Vegas shooting

Federal agents say the FBI has known for several days that the Las Vegas sheriff was providing inaccurate information about the sequence of events inside the Mandalay Bay to the public.
2:00 | 10/10/17

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Transcript for New timeline raises new questions about law enforcement response to Vegas shooting
We turn next here tonight to that new timeline in the las Vegas attack. The sheriff now revealing that the gunman shot the security guard outside his door at least six minutes before he began to fire on concert-goers, not after the after the massacre, as first thought. Here's ABC's chief investigative correspondent Brian Ross tonight. Reporter: The timing of what happened in this hotel hallway is crucial. And tonight, federal agents say the FBI has known for several days that the Las Vegas sheriff had provided inaccurate information. At first, the sheriff's office said Stephen paddock's concert rampage was brought to an end when a security guard showed up on the 32nd floor to check on a door alarm after the shooting had already begun. Paddock fired on him through the door. We believe that he was shooting into the crowd, and then the security officer was shot during that event. Reporter: But that was wrong. Police now concede that security guard Jesus campos called to report he had been shot at least six minutes before the rampage began. A fact the sheriff, under pressure from the FBI, finally acknowledged Monday night. What we have learned is Mr. Campos was encountered by the suspect prior to his shooting to the outside world. Reporter: Tonight, the big question, if the hotel knew there was an active shooter on the 32nd floor, six minutes before the rampage began, could they have done more to stop him? Today, a deputy sheriff told our Las Vegas station, KTNV, the hotel did the best it could. You have that human factor where it goes to a person and they end up logging it into a computer, then they call dispatch at the same time, he may have already started firing outside. Reporter: The owner of the mandalay hotel, mgm, would not answer questions today from ABC news. And David, we know paddock got a number of perks at a high roller, and federal authorities tell us, he was given access to the service elevators, and that allowed him to use -- to bring his cases of weapons up, by passing front lobby security. David?

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

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