NEW YORK (CBSNewYork) – It’s the testimony that could be the key to conviction in one of the city’s biggest murder trials.

A suspect in the killing of Lesandro Guzman-Feliz, known as “Junior”, is now a key witness, CBS2’s Lisa Rozner reported.

On Thursday, Kevin Alvarez faced cross-examination.

The biggest revelation so far is that he’s already pleaded guilty to conspiracy and manslaughter charges.

As part of a plea deal with the Bronx district attorney, he may only be sentenced to time served.

In a surveillance video, Alvarez is the suspect seen in a white shirt dragging 15-year-old “Junior” out of the bodega on East 183rd Street in the Belmont section of the Bronx before others stabbed him with knives and a machete outside.

In contrast to the hoodie he wore during his arrest last year, Alvarez has been showing up to court in preppy clothes, including a plaid button down shirt.

He’s told the prosecutor is putting his life on the line to testify against his former alleged fellow gang members.

The five defendants in this trial are part of a group of 14 that were arrested.

He’s cried and trembled while telling his version of events, including the fact that after “Junior” was killed, some gang members didn’t even know if they got the right guy.

The Trinitarios allegedly believed “Junior” was part of the rival Sunset gang.

Junior’s mom, Leandra Feliz, has been arriving to court and greeted by tons of #JusticeForJunior supporters.

But there’s also been drama for her outside the trial. Tuesday one of the defendant’s family members cursed at “Junior’s” mom in the hallway. Court officers could be seen talking to suspects’ supporters this morning.