Mario D. Cruz, 17, pleaded not guilty to second-degree murder Saturday in First District Court in Central Islip.
Cruz, who appeared in court with several family members, was ordered held without bail.
Cruz and Omar DeJesus Perez Sanchez, of Brentwood, were sitting in a wooded area off Mayflower Avenue on Thursday when they began to argue, Suffolk County Assistant District Attorney Todd Pettigrew said.
Cruz stabbed Sanchez in the chest several times, and after the wounded man fell to the ground, Cruz stabbed him again in the back and head, Pettigrew said.
When questioned by police, Cruz admitted to the stabbing and showed police where he disposed of the knife, the prosecutor said.
Pettigrew gave no information about what kind of knife was used or where it was found. Cruz, a Guatemalan citizen, has no prior convictions in the United States, the prosecutor said.
Defense attorney Richard Stafford of Bohemia said his client has been in Suffolk County for three years.
Of the stabbing, Stafford said, "It's not the way it seems."
Police received a 911 call at 6:52 a.m. Thursday about the discovery of the body in a lot adjacent to a house on Mayflower Avenue.
With Keith Herbert