Flores, now 19, pleaded guilty in Suffolk Superior Court on Thursday to voluntary manslaughter, arson, and attempting to escape, avoiding a first-degree murder trial. He was then sentenced to 15 years in prison, followed by 15 years of probation.

His abuser did not fight back: Instead, he admitted the abuse on camera, wound duct tape around his face, and asked to be strangled instead of slashed to death.

Tortured for years by memories of sexual abuse by a family friend he allegedly suffered, 17-year-old Marco Tulio Flores finally snapped. In a case that prosecutors called “vigilante justice,” he armed himself with a knife, a dog chain, and a video camera, and went to Jaime Galdamez’s East Boston apartment on May 22, 2011.


Flores was just 9 years old when the abuse started, Assistant District Attorney Ian Polumbaum said. When he reached puberty, it stopped, but Galdamez stayed close to his family. Flores never told anyone about the abuse, but when he found a photo of a young relative in Galdamez’s home, he became terrified that Galdamez, 28, was planning to abuse the boy, Polumbaum said.

“The flood broke,’’ said Flores’s lawyer, James Budreau. “The dam broke. He couldn’t stop himself. He did what he did not out of vigilantism, but a perceived threat to these children.”

In a video he made showing himself before and after the death, Flores said he was going to “kill a pervert,” Polumbaum said. When Flores went to Galdamez’s home, he interrogated him on tape about the abuse, which Galdamez first denied, then admitted, Polumbaum said.

Flores gave Galdamez duct tape to put on his face and placed the dog chain around his neck. At one point, Flores appeared to be about to cut Galdamez’s neck, Polumbaum said, but Galdamez said: “Don’t do that. There would be too much blood.” He asked to be strangled instead.


The next video shows Galdamez dead with the chain around his neck, Polumbaum said. Flores sits on the bed next to the body and says, “I can think so much clearer now.”

Flores burned down Galdamez’s home the next morning, but first he removed computers and a television. On the computers, Polumbaum said, investigators found child pornography and chat-room conversations in which Galdamez described his attraction to young boys and talked about Flores.

Flores walked into the East Boston Police Station and confessed to the killing in the early morning hours of May 24, 2011.

“We hope that a 15-year sentence is enough to say we’re not going to give vigilante justice a pass,” Polumbaum said. “I know there are people out there saying, ‘Let him go; don’t prosecute him at all.’ You can’t go out and kill somebody, no matter what he did to you.”

Flores was composed and polite throughout the hearing. As Polumbaum recited the facts of the case, however, Flores appeared at times to fight back tears, blinking rapidly and raising his eyes to the ceiling. Family members and supporters filled the benches, some crying quietly as the sexual abuse was detailed.

The attempt-to-escape charge that Flores pleaded guilty to stemmed from an unsuccessful attempt to flee from Nashua Street Jail in late 2011.

“This was a just resolution to an utterly tragic case,” Suffolk District Attorney Daniel F. Conley said in a statement. “It provides accountability for a life that was taken cruelly, but it also recognizes the strong mitigating factors and the potential outcomes at trial.”


Evan Allen can be reached at evan.allen@globe.com. Follow her on Twitter @evanmallen.