Dallas police Officer Martin Rivera took the stand this week in the Amber Guyger trial, where prosecutors revealed that he and Guyger, his former police partner, had an on-again, off-again sexual relationship.

Rivera has something else in common with Guyger: The 17-year DPD veteran also shot and killed an unarmed man.

On March 22, 2007, Rivera shot 20-year-old Brandon Washington outside a Pleasant Grove convenience store, where the man was eating an allegedly stolen candy bar.

On Wednesday, Brandon's mother, Antoinette Washington, joined a midday news conference in downtown Dallas by Mothers Against Police Brutality to demand that the death of her son be re-investigated.

Members of the group said that Rivera's testimony Monday raised questions about his integrity and that the case preceded new policies in the district attorney's office that independently looked into officer shootings.

"That's something that we had pushed for, and it wasn't until that happened that we began to get any indictments, basically, in fatal shootings," said John Fullinwider, co-founder of Mothers Against Police Brutality.

Antoinette Washington's son, Brandon Washington (pictured in poster), was shot and killed by Dallas police Officer Martin Rivera outside a convenience store after Washington stole a candy bar on March 22, 2007. (Ashley Landis / Staff Photographer)

Antoinette Washington said she had questioned the legitimacy of the investigation into her son's shooting. During the news conference, she broke down in tears as she described the past 12 years without her son.

She said she felt ill after seeing Rivera testify that he deleted his texts with Guyger after the shooting.

"It blew my mind to see him in another case," she said. "I knew he was no good then. Justice has failed."

The Dallas Police Department did not immediately respond to a request for comment Wednesday.

Reached by phone Wednesday, Dallas Police Association President Mike Mata declined to comment, saying he could be called to testify.

Dallas police Officer Martin Rivera, the former police partner of Amber Guyger, reacts as Assistant District Attorney Jason Hermus shows him his texts and Snapchat records while Rivera testifies on the witness stand. (Tom Fox / Staff Photographer)

Washington described her son as a goofy young man who loved to have fun and pull pranks. She said he didn't have a violent history and had gotten in trouble only for criminal trespass. His nickname was "Lil Wimp" because as a baby, he couldn't lift himself up as he crawled.

The night he was killed, Washington was suspected by a clerk of shoplifting a candy bar at a convenience store on Lake June Road in Pleasant Grove, according to news reports.

When Washington was slow to take his hands out of his pockets, Rivera shot him once in the head and leg, police records say. He died later.

No weapon was recovered from Washington, according to news reports at the time. The item in his pocket was a cellphone, his mother said.

In April 2007, funeral services were held for Brandon Washington, who was shot and killed by Dallas police. His aunt, Cynthia Washington (right) was comforted before the service by Katrina Jo Randolph as she viewed Brandon's body. (MONA REEDER / 116916)

A grand jury looked at the case, and Rivera was not charged with a crime.

Collette Flanagan, who helped start MAPB after Dallas police killed her own unarmed son, Clinton Allen, said police officials reported that Rivera thought Washington had a gun. Flanagan said the group wants Rivera “fired immediately," and the Washington case reopened and investigated.

"He's on oath saying he destroyed evidence," Flanagan said. "If you destroyed evidence for your lover, you certainly would destroy it for yourself."

Sara Mokuria, another MAPB founder, said Dallas officers in past decades who killed people were routinely no-billed by grand juries, and the cases need to reviewed.

Before Balch Springs officer Roy Oliver was found guilty of murder in 2018, an officer had not been indicted in Dallas County since 1973. Oliver was sentenced to 15 years in prison for the murder of Jordan Edwards, a 15-year-old boy shot while riding in a car with other teenagers leaving a house party.

More than four decades had passed in Dallas County since another police officer was found guilty of murder in an on-duty shooting.

Santos Rodriguez, who was 12 years old, was shot in the head in 1973 while handcuffed in a Dallas police car after officers picked up him and his brother on suspicion of burglary. Officer Darrell L. Cain interrogated the boy Russian roulette-style, with a gun to his head. Cain was found guilty. He served two-and-a-half years of a five-year prison sentence.

Mokuria said officer fatal shootings deserve to go to trial and have evidence presented to the public. She said in Guyger's case, it revealed the special treatment she received after killing Botham Jean.

"Trials like this are extremely important because they lift the blue veil and show us what's happening in the police department," Mokuria said.