A 20-year-old man in the northern Mexican city of Monterrey has admitted to killing 45 people.
Juan Pablo Vazquez is being investigated for 34 more deaths.
He was caught earlier this month in Monterrey where he was allegedly selling drugs, said Nuevo Leonstate security spokesman Jorge Domene.
Vazquez, who said he was part of an unidentified local organised crime group, has already admitted being behind 45 killings and "is related to at least 79 murders, most of them committed in 2012", Mr Domene told a news conference.
Mexico has suffered from a wave of drug-related violence, with about 1,000 people a month dying in gangland killings. About 80,000 people have died since 2007 in cartel violence.