FILE - In this April 24, 2018 file photo, a protester holds up a piece of cardboard with marked with a -3, in reference to the three film students killed by drug cartel assassins, in Mexico City. Mexican authorities said Thursday, May 10, 2018, that investigators had found DNA from 12 separate people in residual fats found in tanks where one of the killers of the film students confessed to having dissolved bodies in acid. (AP Photo/Eduardo Verdugo, File)

MEXICO CITY - A drug cartel's assassins who killed three film students apparently mistaken for members of a rival gang and dissolved their bodies in acid did the same thing to nine other people, authorities said.

Interior Secretary Alfonso Navarrete said investigators had detected DNA from 12 separate people in residual fats found at a location where one of the killers confessed to having dissolved bodies in sulfuric acid.

Navarrete did not say whether any of the DNA profiles matched those of the three film students who were abducted March 19 on the outskirts of the western city of Guadalajara.

He did say that three of four suspects in the students' abduction and killing had been arrested.

The three students were unwittingly working on a film project for school at a house that was apparently being watched by members of the Jalisco New Generation drug cartel. The house had once been used by a rival drug gang, and the Jalisco cartel apparently suspected the students were part of that gang.

One suspect said the cartel killed the students after interrogating them and then dissolved their bodies.

The DNA findings lent more credence to the tale told by a young rapper who said he had been employed by the cartel to dissolve bodies.

That suspect, Christian Omar Palma Gutierrez, is a 24-year-old rapper who built a YouTube channel with more than a half-million views based on songs describing an anguished, violent life of drugs and crime.

Palma Gutierrez confessed to working for the Jalisco New Generation cartel, Mexico's fastest-growing and most violent gang, as what the gang calls a "cook."

By his account, for 3,000 pesos a week, he dumped bodies head-first into acid baths set up in water tanks in the yard of a cartel safe house. He would come back after two days — after the acid had done its work — and open drain valves to release the fluid into the storm drain, and remove remaining sludge to dump it in fields.

However, some sludge remained in the bottom of the tanks, and that is apparently where investigators found the DNA.

News from © The Associated Press, 2018