Three reputed MS-13 members who are already behind bars on previous charges have been hit with a new indictment alleging that they knifed a 16-year-old rival gang member to death in a park in Queens — and left his body there to be discovered by a bird-watcher.

In an indictment unsealed on Thursday, the US Attorney’s office in Brooklyn alleges that Melvi Amador-Rios, 28, known as “Letal” and “Pinky”; Josue Leiva, a 22-year-old who is also known as “Colocho”; and 24-year-old Luis Rivas, also known as “Inquieto,” stabbed Julio Vasquez to death in May 2017 in a wooded area in Alley Pond Park in eastern Queens.

The trio’s new charges include racketeering, murder, robbery and other charges.

Amador-Rios, alleged to be the head of the MS-13’s Centrales Locos Salvatruchas clique, has been in the slammer since August 2018, when he was picked up on charges that he ordered the murder of a rival gang member. The plot proved unsuccessful, but rendered the target a paraplegic.

In March, Leiva was added to the indictment against Amador-Rios on robbery and firearms charges. Rivas has been locked up since at least October.

While being held in a Tombs jail cell in Manhattan on state charges that include attempted murder, Rivas and two other reputed MS-13 members assaulted an inmate believed to be a member of the rival Latin Kings, according to court papers.

About 20 minutes prior to the beatdown, Rivas was recorded whining to his girlfriend on the phone about life with MS-13 and his directive to assault the rival gang member.

“If not, the one that would be stabbed would be me. I’m telling you that sometimes I feel like taking my own damn life,” he said in Spanish, according to court papers. “This thing is garbage.”

The teen’s body was discovered by a 52-year-old bird-watcher who stumbled on the corpse at Alley Pond Park near 76th Avenue in May of 2017.