MARTINEZ -- A Contra Costa jury on Tuesday found a 37-year-old Richmond man guilty of first-degree murder in the fatal shooting of a romantic rival last year.

Oscar Carrillo faces 50 years to life in prison for killing 21-year-old San Pablo resident Jose Marroquin Flores on March 25, 2011, outside their boxing trainer's Richmond home on 38th Street.

Carrillo and Marroquin Flores both trained at King's Boxing Gym in Oakland and frequently carpooled there with their trainer. Marroquin Flores, a landscaper from El Salvador, aspired to be a professional boxer and was getting ready for a big fight.

The victim was sitting in his car when Carrillo sneaked up from behind and shot him in the back of the head. He planned the killing because a woman from the gym had chosen to date Marroquin Flores over himself, deputy district attorney Molly Manoukian told jurors. The murder happened two days after Carrillo spotted the new couple hugging and kissing outside the gym and became visibly enraged.

Both Marroquin Flores and the woman were troubled by Carrillo's reaction to their budding romance. Marroquin Flores had tried to smooth things over with Carrillo but was unsuccessful, Manoukian said.

Speaking after the verdict Tuesday, the prosecutor described Marroquin Flores as a "true innocent."

"The victim was a very nice young man," Manoukian said. "Everyone really loved him."

Carrillo's attorney argued at trial that the shooting was

Carrillo was waiting for Marroquin Flores to drive him to the gym when he showed the victim his .40-caliber pistol, defense attorney Joseph Tully said. Carrillo's hand slipped while unloading the gun, causing it to fire.

Tully said Carrillo considered the victim a friend and was devastated by what happened and fled the scene because he was in shock.

Carrillo is scheduled to be sentenced by Judge Barbara Zuniga on Aug. 1.

Contact Malaika Fraley at 925-234-1684. Follow her at Twitter.com/malaikafraley.