He is believed to be among five killed by the Mexican army over the weekend.
Mellado is accused of being an original member of the Zetas, an offshoot of the Gulf cartel. Their rivalry is considered responsible for the violence in the area, notorious for actions such as decapitation of enemies. The battle between the Gulf cartel and the Zetas turned Tamaulipas into one of Mexico's most violent states.
Mellado was killed after escaping from prison, where he was jailed after armed robbery, rape and murder accusations, a Tamaulipas official said. He was found in a raid on his hideout in the city of Reynosa that killed four other armed men and one soldier.
Earlier this year, the man regarded as the world's most wanted drug lord, Joaquin "Shorty" Guzman, was arrested in Mexico, and Zetas leader Miguel Angel Trevino was killed in 2013.