The students were kidnapped by at least six people after their auto broke down.
Christian Omar Palma Gutierrez AKA QBA pleaded guilty to the deaths of Salomon Aceves Gastelum, 25, Daniel Diaz, 20, and Marco Avalos, 20.
He claims he was paid 3,000 pesos (£116 / $160) a week by the cartel to work for them and says he had been working for them around three months when he was asked to help get rid of three bodies. Chief investigator Lizette Torres said QBA has participated in three other previous murders and will be charged with aggravated kidnapping in connection to this case.
Gutierrez has a large social media following with his YouTube channel having almost 125,000 subscribers and millions of views for his videos.
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Others show images of young gang members in poor neighborhoods brandishing weapons and taking drugs.
The three victims had been filming a school project at a former hangout for members of the Nueva Plaza gang in Jalisco when they were abducted in March, according to Mexican prosecutors. He also has two Facebook accounts with 140,000 followers combined.
In songs with titles such as "Death Has No Schedule", Gutierrez sings about violence, weapons and drugs, nearly always in a threatening tone.
Officials are reportedly investigating the videos for further clues into the murders, according to AFP.
Juan Martin Perez, the director of a non-governmental organization called Rights to Childhood, called youth disappearance an "epidemic" - contending that organized crime, lack of protection by the government, corruption and authorities' complicity with criminal groups in some locations are to blame.