John Alessio was conducting a regular traffic stop the night of Oct. 1 when he heard something disturbing over his radio. The Las Vegas Metropolitan Police officer had to leave abruptly to rally with his squad and others. On his way there, when he got back in his car, he could hardly believe what he was hearing over the channel.

“It’s almost like it can’t be true,” Alessio told Ariel Helwani on Monday’s edition of The MMA Hour. “It was like, is this a drill?”

The sound of semi-automatic gunfire rang out on the Las Vegas Strip that night. A man opened fire with multiple guns onto a crowd below attending a country-music festival from the 32nd floor of the Mandalay Bay hotel. Alessio didn’t know it yet, but 58 people would die in that crowd and more than 500 ended up being injured.

Alessio and his squad grabbed extra equipment and headed to their assigned spot: Sunrise Hospital. With victims of the senseless shooting streaming in, police officials felt that could be a target at a time when very little was known about what was happening. It didn’t end up being that, but Alessio and his fellow officers were instrumental in helping people at the hospital.

“It almost reminded me of a war movie when you see nurses and doctors trying to triage people, not even getting them into the hospital yet and they’re working on them,” said Alessio, a veteran of 17 years in MMA. “That’s what was there. Definitely very unforgettable. Chaos. The poor people’s families that were there that didn’t get injured that were in a panic. Yeah, I’ll never forget that night right there.”

The gunman, 64-year-old Stephen Paddock, shot and killed himself before police could reach him in the hotel room. A motive for the killings remains unknown more than a week after the massacre. Part of Alessio wishes he could have been there at Mandalay Bay that night, he said.

“Inside, do I wish I go to go right down to the scene?” Alessio said. “I wish I could have gone onto the 32nd floor and taken care of business, but every officer, every squad had a role to play, whether it was just stay in your area and do your regular calls for service or, for example, us we had to go to the hospital.”

What he witnessed, Alessio said, was heartbreaking. But there were also moments that were uplifting. The way people remained unified, he said, will stick with him for a long time.

“It was crazy to see the citizens come together that night, all the heroes that were just there attending, helping other people out, bringing them to the hospital,” Alessio said. “It was a country festival, so I’m seeing guys in jeans and cowboy boots and no shirts on just helping people. But it was awesome to see that people can come together in a moment like this, especially with this country right now, the politics and everybody being divided and all this stuff. That one moment, it didn’t matter. Everybody came together and that was pretty touching to see firsthand right there.”

Alessio, 38, said he began work at 4 p.m. for his regular shift that night and didn’t get back to the station until 8 a.m. He did the same thing the next four days — essentially 16-hour shifts. And even when he was off work, sleep did not come easy. Alessio said he had to be fueled by Red Bull, Monster Energy drinks and coffee.

“By the time I got home and crawled into bed, I think I just lied their awake for hours and hours and hours,” Alessio said of the first night. … “There was very little sleep. Even when we got off shift to go home to go to bed, your mind is just not, ‘Oh I’m going to go to sleep and just turn off what happened in the world.’”

Alessio was in a familiar place Saturday night, sitting near the cage at UFC 216 at T-Mobile Arena. UFC exec Reed Harris, Alessio’s former WEC promoter, helped hook him up with good seats. Alessio praised the job the UFC did in honoring first responders and those affected by the heinous shooting, including bringing them into the Octagon for a singing of America The Beautiful by Everlast.

“I kind of thought they would,” Alessio said of the UFC. “This is their city, this is where they live and this is where UFC is based out of.”

Alessio fought for the UFC, Pride, WEC, Bellator and many more promotions in his long MMA career that goes back to 1998. The Vancouver native said he wanted to try and make two decades in the sport, but was already in the police academy and “it was time.”

Being a police officer is difficult just about every day and he admitted that it has been tougher lately with some things going on in the country. But he said in the last week the Las Vegas community has been incredible. The station briefing room is filled with food and drinks from casino employees and regular citizens.

Oct. 1, 2017 is a date that will infamous for Las Vegas and its residents for generations to come. And Alessio, there that night, helping victims, will have it committed to memory forever.

“I’m never gonna forget this,” Alessio said. “This moment that I’ll never forget. I couldn't imagine what some of the other officers had to go through that night as well. I'm sure everybody is a little bit scarred from this, especially if you lost somebody. I'm sure they're feeling so much more than what I am. I know that we’re just gonna move forward.”