Police arrested 13 members of the gang MS-13 in connection with at least seven murders outside of New York City in the town of Brentwood, Long Island. Among the killings were those of teenage girls Nisa Mickens, 15, and Kayla Cuevas, 16, whose bodies were found in September 2016, officials said at a press conference Thursday.

“For far too long on Long Island, MS-13 has been meting out its own version of the death penalty against members of their gang who violate their so-called ‘rules,’ against rival gang members they seek to eliminate over disputes, and anyone else they decide they want to seek revenge against for any reason they so choose,” Robert Capers, U.S. Attorney for the Eastern District of New York, said during the press conference.

The 13 unidentified members were set to be charged with seven murders and a number of other indictments including racketeering, assault, arson, conspiracy to distribute marijuana and possession of firearms, CBS reported. Ten of the arrested were in the country illegally, while two had green cards and one was a U.S. citizen, police said.

The bodies of Mickens and Cuevas were found just one day apart in Brentwood. Police said both had been severely beaten—Mickens to the point of being unrecognizable.

“The murders of these teens are particularly disturbing,” said Capers. Officials said Cuevas had been “marked for death” because she fought with a gang member on some form of social media, while Mickens had merely been killed because she was hanging out with Cuevas, her lifelong friend.

MS-13, which stands for Mara Salvatrucha, consists of "mostly Salvadoran nationals or first generational Salvadoran-Americans, but also Hondurans, Guatemalans, Mexicans and other Central and South American immigrants," according to the FBI. Founded in Los Angeles in the 1980s, the gang now operates in an estimated 42 states and includes up to 10,000 members.

RTX2H9I2 Police arrest a suspected member of MS-13 during a raid in Tegucigalpa, Honduras, Jun. 20, 2016. Photo: Reuters