The body of Lee Manuel Viloria-Paulino, 16, was found on Thursday.

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A 15-year-old pleaded not guilty to murdering his classmate on Monday in the decapitation of a Lawrence teenager.

 

Mathew Borges was ordered held without bail in Lawrence District Court, charged with the killing of 16-year-old Lee Manuel Viloria-Paulino.The headless body of Viloria-Paulino was found Thursday by a woman walking her dog along the Merrimack River in Lawrence.

 

He had been missing since Nov. 18.

 

RELATED:Decapitated body found in Lawrence identified as missing 16 year old

 

“This is a tragic loss for his family and friends,”Essex District Attorney Jonathan Blodgett said in a statement on Friday.

Borges was arrested on Saturday in connection with the killing. Massachusetts law states that any juvenile 14 or older is treated as an adult if charged with first-degree murder.

Blodgettsaid he believed the two boys went to high school together, but would not speculate as to motive yet.

Borges allegedly confided in a friend that he "did something bad," a person told investigators, according to court documents.

RELATED:Teen arrested in connection with headless body found in Lawrence: DA

"Mathew then told him that he stabbed a kid and cut his head off, killing him," the document reads. "When Mathew said this, he was motioning with his hands as if he was stabbing someone and cutting someone's head off. Mathew then walked out of the house."

Borges is due back in court on Jan. 10.