The three men killed in a brutal attack this week inside a Waltham apartment died from “sharp force injuries of the neck,” the district attorney’s office said today in a statement.

A spokeswoman for Middlesex District Attorney Gerard T. Leone Jr. declined to elaborate on the press release, which also stated that the deaths were determined to be homicides.

A law enforcement source with knowledge of the investigation said each man’s throat was cut during the attack on Monday.

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The victims have been identified as Brendan Mess, 25, of Waltham; Erik Weissman, 31, of Cambridge; and Raphael Teken, 37, of Cambridge. Mess lived at the apartment on Harding Avenue where the men were found.

Authorities have not released a motive for the attack, except to say that it was targeted. Neighbors told the Globe earlier this week that police had indicated to them that the murders were believed to be drug-related.