Transcript for Questions remain unanswered about Las Vegas shooting timeline: Part 1
Reporter: This week in Vegas, it's been business as usual. The party is rocking io the night. But 15 miles from the glitz of the strip, Russell Bleck is up and awake for a different reason. I have literally five nightmares a night, I've counted. And I can't break the cycle. Reporter: Bleck and his fiance Breanna are two of the many survivors of the mass shooting at the route 91 festival. Bleck famously captured some of it on his cell phone. That was an ar! Reporter: And though the shooting stopped nearly four weeks ago, for him and so many others, the incident isn't over. I wake up from a nightmare and just ran down this hallway. I'll just run into this closet and shut the lights off and shut the door and put my body against it so no one can't kind of come in and -- Reporter: His fiance was too emotional to even to speak us. It took me two weeks, three weeks now to be able to look at her. And just, the sheer fear you know, on her face, that's something that you're never going to forget. Reporter: But Bleck is troubled by more than the visceral memories he has of that night. Like other survivors we spoke to, he's also disturbed by what he considers the lingering questions, the missing answers about what really happened. The question that troubles me the most is the timeline, I want to know what happened. Reporter: The official timeline has changed at least three times. It just doesn't make any sense. Because these things are pretty basic. The word incompetence has been brought forward and I'm absolutely offended with the characterization. Reporter: And just this week, the New York Times came out with its own timeline. By forensically analyzing these clips, we were able to draw perhaps the most complete picture to date of what happened. Reporter: Remarkably, it took authorities some time to figure out even when paddock first checked in to the mandalay bay. Originally, it was on September 28th and then it shifted to September 25th. He changes rooms, it sounds like. Did he decide, "I want a room on a different floor, for the different angle?" That's entirely possible. Reporter: But the center of the timeline controversy revolves around this man, security officer Jesus campos, who was shot by paddock through his hotel suite door. But exactly when? In the first official version of events campos encounters paddock at the end of his shooting rampage perhaps preventing further loss of life. Reporter: I'll just reaffirm to you that Jesus campos is a true hero. But that turned out to be not the case. It is, I will just say, out right odd to say someone is a hero who stopped this shooting when now it appears that's really not the case. Why is that so difficult to figure out? Reporter: Campos is shot at 9:59 pm, a full six minutes before the shooting spree began. It didn't make sense at the time because, you know, if you're a gunman who has prepared for months, why would you wait six minutes after having your plans interrupted by a hotel security officer to then start firing on the crowd? Reporter: Third and final version for now the police in the hotel say campos was shot at about the same time as the shooting unfolded. That New York Times' video timeline provides some additional clues as to the possible timing. In the first burst, the gunman fires around 60 bullets of a 100 capacity magazine. There's a pause then of around 36 seconds. We do know that the hotel security officer is in the hallway in or around that time. Perhaps a gun jammed. Or perhaps he used the remainder of that cartridge on this, the hotel security officer. Yet we still don't know if he was shot before or after paddock first turned his guns on the crowd. Tonight "20/20" has what no one has heard before, the voice of campos reporting the shots that fateful night. There's shots fired in 32-135. Reporter: But mgm did not tell ABC news the time that call came through. I'm a big baffled as to why we don't actually know this is what happened. Reporter: There's also an interesting detail posed by the New York Times' timeline, paddock appears to initially fire just single shots. Listen. Some theories are that he's checking his trajectory or that he's firing on fuel stores at the nearby airport. Reporter: The police response has come under scrutiny. Two officers arrived on the 31st floor at 10:12:00 P.M. One floor below paddock three minutes before the shooting stopped. I can hear the automatic fire one floor below us. Reporter: Why are they on the 31st floor, not on the 32nd? When you have an active shooter or a threat somewhere in the hotel you wanna block that off. Reporter: Seal it off. Don't let that threat or that person, in this case paddock, get outside of the 32nd floor so that might've been what they were thinking. Come to the 31st floor. And come up with their plan on how they were gonna come up to the 32nd floor. Reporter: Finally, one the most troubling questions. Why did it take nearly an hour for police to breach paddock's door? Which could have been plenty of time for him to perpetrate further violence. Breach, breach, breach. The reason that you wait is because the eminent threat has either stopped or temporarily stopped. He's not firin' anymore. So at that point they were probably assembling more resources, get the right tactical gear, get the explosive entry equipment. We still don't know why paddock stopped firing, but for the first time we hear what maybe the shots that ended his life. We received another video that films that 12th burst of fire, but also what appears to be two single rounds of fire, about a minute afterwards. Was he taking one last shot at the door or outside, aiming at somebody and then saying, "Now it's my turn." Reporter: Perhaps one day it'll all make sense to Russell Bleck and the other survivors. Then I can hopefully get some rest. Reporter: The experience has marked him for life and while there's plenty of sorrow, there's also strength. It's a constant reminder, you know? I'm never forgetting what happened that day.
This transcript has been automatically generated and may not be 100% accurate.