At the Route 91 Harvest Festival in Las Vegas Sunday night, a gunman killed at least 59 people and injured over 500 when he opened fire from his hotel room at the Mandalay Bay Resort. One of those people he killed was Rachel Parker.

Parker graduated from Cheney High School in 2002, and lived in California where she worked as a police officer for the Manhattan Police Department. She was 33.

The gunman used his 23 guns he had with him in his room on the 32nd floor of Mandalay Bay where he was across the street from the concert and had a bird’s-eye view of the 22,000 concert goers.

The three-day Harvest Festival was just about coming to an end when Jason Aldean took the stage. During his performance the shooter opened fire.

“It sounded like two firecrackers going off,” said Mark Gray, a writer for the Rolling Stone who was in attendance. “[I] looked up at Mandalay Bay and saw a light flickering, while shots were still ringing out.”

Videos taken during the time of the shooting show that most of the people thought the same thing before they realized it was gunshots going off, not fireworks.

The incident is now considered the deadliest mass shooting in United States history.