Prosecution testimony is under way in the trial of a Chelsea man accused of stabbing 22-year-old Luis Garcia-Calle outside a Williams Street bar last year, causing injuries that killed the East Boston man in his hospital bed weeks later.

MARIO MARTINEZ BONILLA (D.O.B. 6/1/86) is charged with first-degree murder. His trial in Suffolk Superior Court began with jury selection yesterday and lawyers’ opening statements today.

Suffolk homicide prosecutors expect to prove that Bonilla engaged the victim and others in a verbal altercation at the El Carriel bar at about 10:00 p.m. on Feb. 27, 2008. As a result of that altercation, bar staff asked him to leave and he refused. Garcia-Calle then joined the staff in asking Bonilla to leave.

“I’ll be outside,” Bonilla allegedly said as he left.

Garcia-Calle left the barroom and went outside. A fistfight erupted between the two men in the parking lot. Two witnesses are said to have seen Bonilla striking Garcia-Calle, who then staggered back into the bar as Bonilla fled the scene. Garcia-Calle was suffering from multiple stab wounds and was rushed to Massachusetts General Hospital for treatment. He remained there until he succumbed to his injuries on March 17, 2008.

The assailant was unknown to any of the bar staff or the victim himself at the time of the incident. Armed with a description but not a name, Chelsea Police – and, later, State Police detectives with jurisdiction over all homicides in Chelsea, Revere, and Winthrop – undertook a far-reaching investigation, conducting multiple interviews and urging anyone with information on the case to come forward.

On June 5, 2008, however, Bonilla returned to El Carriel and began drinking heavily. Bar staff recognized him as the man who had fought with Garcia-Calle and called police; when they arrived, he was so intoxicated that he could not speak with them. He was taken into protective custody. In the days that followed, investigators obtained multiple identifications of Bonilla as the assailant and Suffolk prosecutors approved a warrant charging him with murder on June 10.

Assistant District Attorney Ian Polumbaum of the Suffolk DA’s Homicide Unit is trying the case. Eliany Colon-Vargas is the assigned victim-witness advocate. Bonilla is represented by attorney Michael Laurano. Testimony is ongoing before Judge Charles Spurlock in courtroom 808 of Suffolk Superior Court.