At first, it sounded like a jackhammer.

That was Jason Hartman's first thought as he and a friend were on the balcony of a hotel room at the Mandalay Bay Resort Casino. Hartman, a real estate investor, was in Vegas to attend a business conference.

"Right as we walked out onto the balcony, we heard shooting. I heard the shots and it sounded kind of like a jackhammer," Hartman said. After a few moments, they realized it was gunshots. They watched as people began running and falling to the ground.

"It was very, very loud the way it echoed through the building," he said. "More shots rang out, and more shots rang out."

Hartman and his friend decided to exit the hotel. "I saw police running through the lobby with machine guns, regular cops with machine guns. That's when I realized this was a mass shooting."

He said when he got into his car, he saw all the police cars. "They were coming in every direction. They were blocking roads, barricading, forming a perimeter, they were closing bridges. There were just police everywhere. Then the ambulances. There was ambulance after ambulance coming toward that scene as we were going away from it."

 The Oct. 1 massacre left 58 people dead and more than 500 others injured. Authorities say 64-year-old Stephen Paddock of Mesquite, Nevada sprayed bullets into a crowd attending the Route 91 Harvest music festival on the Las Vegas Strip from the 32nd floor of the hotel between 10:05 and 10:15 p.m, eventually killing himself.

"I was 25 floors above the shooter," Hartman said. "I was that close."

Paddock may have researched the possibility of attacking other outdoor concerts, including the Lollapalooza festival in Chicago in August 2017, according to several news sources. Paddock "had his sights set on Lollapalooza in Chicago and even booked 2 rooms in a hotel that overlooked the massive outdoor venue," TMZ reported.

The week before the shooting, Paddock booked an apartment at The Ogden in Downtown Las Vegas, which overlooked the open-air Life Is Beautiful festival and arrived at the Mandalay Bay hotel Sept. 25. Clark County Sheriff Joe Lombardo said Paddock carried more than ten suitcases into his hotel suite during his preparation for the shooting.

Twenty-three firearms, a large quantity of ammunition, and numerous high-capacity magazines capable of holding up to 100 rounds apiece were found in Paddock's suite, according to reports.

At a press conference on October 4, Sheriff Lombardo stated there was evidence showing Paddock had intended to escape the scene, and that he may have had assistance from an accomplice.

That's something Hartman believes as well. "The shots sounded like they were coming from different directions," Hartman said, noting that he's not a conspiracy theorist nor an expert.

The hotel was locked down after Hartman left. Another friend, Larry, didn't leave and was locked in, having to spend the night in a meeting room. Larry, whose last name was not provided, was not a guest at the hotel but rather had been an attendee at a meeting. On the inside, Larry said they were receiving conflicting reports and presumed it was a terrorist attack. He added that there was a lot of commotion outside of the room, which was on the 64th floor.

Larry said there was a lot of panic in the room. The SWAT Team showed up and had everyone put their hands above their heads, not knowing if one of them was involved with the shootings. Eventually, they were moved to another room.

"It was a high-stress situation," Larry said. He added that when they were in the larger room, some were calm and others remained panic. "You saw the range of the human emotion in that room."

He and the other 60-80 people were allowed to leave around 7:45 the next morning.

Hartman said he has nightmares about it and can't imagine what it's like for those who were present at the concert. "This changed me forever," he said.

Hartman's video of the shootings can be seen here.