Christopher Roybal was celebrating his birthday Sunday with his mother, Debby Allen, when the cracking of rounds began cutting through the bewildered crowd at the Route 91 Harvest country music festival.

Roybal, 28, a Navy veteran from Corona, California, was struck in the chest by a round fired from the 32nd-story window of the Mandalay Bay Resort and Casino, where 64-year-old Stephen Paddock began firing into the crowd of about 22,000, the Washington Post reports.

A fireman who was with Roybal when he was shot attempted to save him, but couldn’t revive him in the midst of the chaos, Allen told KABC.

“He saw Christopher take his last breath,” Allen said.

Roybal is one of at least 59 people killed in what is now the deadliest shooting in U.S. history.

After enlisting in the Navy in 2007, Roybal rotated through duty stations such as Fleet Activities Yokosuka, Japan, and Naval Base Kitsap, Washington.

While attached to the Army’s 25th Infantry Division in Kandahar, Afghanistan, MA3 Roybal served as an explosive detector dog handler, according to a report by Business Insider.

His final Facebook post recalled the harrowing moments service members experience in a firefight.

"What's it like being shot at?" A question people ask because it's something that less that 1% of our American...

Posted by Christopher Roybal on Tuesday, July 18, 2017

Roybal’s awards include an Army Commendation Medal, a Combat Action Ribbon, a Good Conduct Medal and an Afghanistan Campaign Medal, among others.

He would have turned 29 on Oct. 9.

“Today is the saddest day of my life,” Allen wrote on Facebook. “My son Christopher Roybal was murdered last night in Las Vegas. My heart is broken into a billion pieces.”