Statements from a suspect confirm that the May 26 kidnapping of 13 people from a Mexico City bar and their subsequent murder was an instance of score-settling between criminal groups, capital district attorney Rodolfo Rios said.
Joel Eduardo Galicia Espindola told investigators he and several accomplices acted "to avenge" the murder of their associate Horacio Vite Angel, Rios said.
Galicia admitted his participation in the mass abduction at Heaven, a bar in Mexico City's upscale Zona Rosa district, the prosecutor said at a press conference.
Authorities have been saying that the crime was carried out in reprisal for the May 24 killing of Vite Angel, a reputed member of the La Union de Insurgentes drug gang, by the rival La Union de Tepito group.
One of the people taken from the bar and killed, 16-year-old Jerzy Ortiz, was the son of Jorge "El Tanque" Ortiz Reyes, the jailed boss of La Union de Tepito.
The bodies of the people snatched from the Heaven bar were discovered last month by federal authorities pursuing leads in a firearms case unrelated to the kidnappings.
Investigators found the mass grave - covered with cement, asbestos and lime - on the La Mesa ranch in Tlalmanalco, Mexico state.
Autopsy results and other forensic evidence indicates the victims were killed within hours of their abduction, according to Rios.
Of the 19 people arrested so far in connection with the case, a dozen remain in custody and seven have been formally charged, Rios' office said. EFE