A Salem man who spent nearly three years on the run was convicted Wednesday of fatally shooting a combat veteran from Revere in Boston’s Theatre District in 2012.

Suffolk Superior Court jurors convicted Peter Castillo, 28, of first-degree murder for the slaying of US Army veteran Stephen Perez Jr., 22, District Attorney Daniel F. Conley’s office said.

Castillo faces a mandatory life term without the possibility of parole when he is sentenced Monday. His lawyer, Scott Gleason, did not immediately respond to inquiries seeking comment.

“Cases like this are the reason we take a hard line against illegal handguns in Boston,’’ Conley said in a statement. “A young man carrying an illegal handgun isn’t just more likely to use it — he’s more likely to put himself in the position where he’ll use it. This was an argument, a fistfight at the most, that escalated to murder because the defendant was carrying a handgun he had no business possessing.’’

Conley said the “terrible irony is that Stephen Perez survived two tours of duty in Afghanistan only to die on the streets of Boston.’’

Prosecutors said Perez was out with friends in the early morning hours of April 28, 2012, when he became involved in an altercation in a Tremont Street parking lot, and Castillo shot him in the back.

Perez had served as an Army sniper and came home to Revere determined to become a federal law enforcement officer, family and friends told the Globe shortly after his death. He was studying at Bunker Hill Community College and planned to transfer to Boston University.

Relatives of Perez could not be reached for comment on Wednesday.

Castillo was quickly identified as the suspected gunman, based on evidence including video footage and witness statements, according to authorities. But he fled to New York City the day after the shooting and boarded a flight to the Dominican Republic, where he was arrested in January 2015.

He had been on the US Marshals Service’s “15 Most Wanted’’ fugitives list before he was apprehended.

Two additional defendants, Luis Sepulveda, 32, and Janice Hardy, 25, both of Lynn, will be tried at a later date for allegedly lying to police and a grand jury investigating the murder, Conley’s office said.

Laura Crimaldi of the Globe Staff contributed to this report. Travis Andersen can be reached at travis.andersen@globe.com. Follow him on Twitter @TAGlobe.