Three Mexican film students who went missing five weeks ago were kidnapped, tortured, killed and likely dissolved in acid, investigators have said, a gruesome end to a case that triggered vehement protests. The students - Salomon Aceves Gastelum, 25; Daniel Diaz, 20; and Marco Avalos, 20 - went missing on March 19 as they returned from shooting a film project outside Guadalajara, Mexico's second city, where they attended the University of Audiovisual Media. Witnesses said they were intercepted by a group of six to eight men who forced them into another car and fled. The case drew outraged protests from their fellow students, backed by Mexican film luminaries such as Oscar-winning directors Guillermo del Toro and Alfonso Cuaron. There are currently more than 33,000 people missing in Mexico, a number that has exploded along with the murder rate as the country struggles to rein in brutal violence linked to drug trafficking. Missing persons cases often go unsolved, in a country where more than 90 per cent of violent crimes are never punished. The most notable example is the disappearance and feared massacre in 2014 of 43 students who were studying to be teachers in the southern state of Guerrero. Chief investigator Lizette Torres said the film students' kidnappers are believed to belong to the Jalisco New Generation drug cartel, a powerful crime syndicate based in the western state where they studied. "There is no indication that (the students) themselves had any link with any cartel," she told journalists. Investigators believe one of the students had a relative involved in a rival cartel and that they may have been murdered in a revenge killing, she said. The confirmation of their death came after investigators seized three barrels filled with acid from a house in the city of Tonala, where the students had been filming. DNA tests will be carried out to determine whether the students' bodies were dissolved in the acid, Torres said.