Two members of the violent MS-13 street gang were convicted of executing a father as he celebrated his birthday in San Francisco’s Mission District nearly three years ago, prosecutors said Friday.

The San Francisco Superior Court jury deliberated for three days before returning guilty verdicts Thursday against Jose Mejia-Carrillo, 24, and Alexis Cruz-Zepeda, 25, in the March 17, 2017, killing of George Martinez.

Mejia-Carrillo was found guilty of first-degree murder and being a felon in possession of a firearm, along with gun and gang enhancements. Cruz-Zepeda was found guilty of one count of criminal street gang conspiracy for acting as the lookout and distracting Martinez while Mejia-Carrillo fired the deadly shots.

The verdict “brings long-awaited justice to the victim and his family and represents a line in the sand that brazen gang violence of this nature will not be tolerated in this community,” Assistant District Attorney Adam Maldonado said.

The case centered around the defendants’ participation in the 20th Street clique of the brutal Mara Salvatrucha gang, known as MS-13. Maldonado described how the killing was part of a larger effort by the gang to become more powerful by using violence to spread fear in the neighborhood.

The trial may be the last case with gang enhancements charged by the district attorney’s office for the foreseeable future. The incoming district attorney, Chesa Boudin, has pledged to stop charging gang enhancements when he takes office Jan. 8, citing stark racial disparities in how the law is applied.

Gang enhancements, which add additional years to a sentence for an underlying felony, make communities less safe by creating tension between law enforcement and minority neighborhoods, Boudin said during his campaign for district attorney.

He said he will continue to charge defendants with violent crimes. Martinez’s killers likely would still have faced harsh punishments even without the gang allegations.

The night of the murder, Martinez, 44, was with his adult son at the Beauty Bar on 19th and Mission streets. The men had been at a Warriors game in Oakland and decided to stop by the bar on the way back to their San Bruno home.

Little did they know, prosecutors said, MS-13 members were in the bar and mistook Martinez as a rival gang member. Mejia-Carrillo and Cruz-Zepeda followed Martinez out of the bar as he and another man got into a car on 19th Street.

Mejia-Carrillo was captured on security video crouching next to a car behind the vehicle while Cruz-Zepeda walked by smoking a cigarette.

Martinez got out of the car and briefly spoke to Cruz-Zepeda as Mejia-Carrillo sneaked up from behind and shot him in the back before putting a second bullet in his head. The execution was captured by a nearby market’s security camera.

Prosecutors said Mejia-Carrillo fled the scene on foot, dropping his cell phone and ditching the murder weapon in a trash bin in a dark corner of a nearby parking lot. When investigators searched the phone, they found selfie videos of Mejia-Carrillo flashing MS-13 gang signs while riding BART a week before the shooting.

A witness described hearing someone ask Martinez if he was a Norteño, a gang rival of MS-13, seconds before the shooting.

Investigators later found Mejia-Carrillo’s DNA on the murder weapon, prosecutors said.

Since being arrested, Cruz-Zepeda has gotten several tattoos while in San Francisco Jail, including “MS-13” on his hand and devil horns — a common symbol of the gang — on his arm.

Mejia-Carrillo’s attorney, Deputy Public Defender Steve Olmo, argued that his client wasn’t the killer. He said none of the videos showed his client’s face. Cruz-Zepeda’s attorney, George Borges, said in court that his client was present but wasn’t part of the conspiracy.

Weeks after the killing, someone sprayed graffiti on a wall across from where Martinez was shot. Prosecutors said the vandalism was done by MS-13 in celebration of the violence.

“When gang members commit crimes, it’s a universe of difference from when normal people commit crimes,” Maldonado told the jury during his closing arguments on Monday.

Interim District Attorney Suzy Loftus on Friday thanked Maldonado and investigators in the case, including San Francisco police sergeants Robert Trujillo with the Gang Task Force and Jon Kasper with the Homicide Bureau.

“A young father was murdered and his family has suffered an unimaginable loss,” Loftus said. “We are going to make sure that these individuals are never able to harm anyone else in our community ever again.”

Evan Sernoffsky is a San Francisco Chronicle staff writer. Email: esernoffsky@sfchronicle.com Twitter: @EvanSernoffsky