Mexican security forces have arrested a 56-year-old suspect wanted in connection with the killing of 72 migrants in 2010.
The migrants from South and Central America had been kidnapped by the Zetas gang and taken to a ranch.
A survivor told police that, when they refused to work for the gang, the 58 men and 14 women were killed.
The suspect, Martiniano Jaramillo, was arrested at a hospital in Ciudad Victoria, in northern Mexico.
Investigators say he was in charge of the Zetas gang in the region of San Fernando when the migrants were seized and killed.
He is also accused of ordering other kidnappings and killings in the area, including that of Miriam Rodríguez, a Mexican activist who was investigating her daughter's killing when she was herself murdered.
Read: Mexican mother who probed daughter's death is killed
The security forces said that extensive field and detective work had enabled them to identify and trace Martiniano Jaramillo to the hospital where he was receiving treatment.
The killing of the 72 Central and South Americans drew international attention to the dangers facing migrants trying to reach the United States via Mexico.
It also shone a spotlight on the Zetas drugs gang and their cruel tactics.