Stanley Juarez is accused of fatally stabbing 18-year-old Bryan Lemus, who went missing in August 2016.
Police believe Juarez and other members of MS-13 killed Lemus because, although Lemus had previously associated with the gang, members began to believe Lemus was a threat to them.
"He associated with gang members," Nassau police Detective Lieutenant Stephen Fitzpatrick said. "For some reason, they felt that he was an enemy of their particular clique, and thus he was marked for death at that point."
Authorities say Lemus was hacked with machetes and buried in a shallow grave in the Massapequa Preserve, where his remains were discovered last Friday.
"This police department doggedly made sure that we were able to tell a family that we've identified the remains of their loved one," District Attorney Madeline Singas said.
Nassau Police Commissioner Patrick Ryder said homicide detectives never gave up hope that they would discover Lemus' remains.
"They went out and raked leaves and dug holes," he said. "We had backhoes out there. We were going to find the remains, return to the family and make sure this prosecution sticks."
Juarez was already in prison for a stabbing attack at Hempstead Lake State Park last year. He is charged with second-degree murder in Lemus' death.
Police said more arrests may be made in Lemus' murder.
"We are expecting to be charging others in the very near future as the investigation continues," Ryder said.
WATCH: Authorities announce arrest of Stanley Juarez
June 6 update: Police announced that 19-year-old Raul Ponce has been arrested and charged with two counts of second-degree murder in this case.
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