Mexican police have captured an alleged former Sinaloa drug cartel lieutenant accused of being involved in the killings of more than 350 people found in mass graves in 2011.
Police in the northern state of Chihuahua detained Mario Nunez, 39, also known as "M-10", on Wednesday in the border city of Ciudad Juarez, federal security spokesman Eduardo Sanchez said.
Nunez, a former police officer, began working with the Juarez Cartel before joining the rival Sinaloa organisation allegedly led by Mexico's most-wanted man, Joaquin Guzman.
The government partially blames Nunez for an upsurge in drug violence that brought shoot-outs in broad daylight, ambushes of police and kidnappings to Ciudad Juarez, which is across from El Paso, Texas.
US court documents say Guzman, known as "El Chapo", hired Nunez and gave him the job of snatching the smuggling corridors into the US from the local Juarez Cartel, through ordering gangs of hitmen to carry out killings that included grisly mutilations and decapitations.
The Juarez Cartel lost ground to the Sinaloa organisation in a three-year battle that wound down in 2011. But Nunez's criminal career continued, authorities say.
The Mexican government claims Nunez's power struggle with another drug chieftain in the spring of 2011 resulted in the murder of 350 people, whose bodies were unearthed in 23 mass graves in the northern state of Durango.
"Much of the violence seen in the states of Chihuahua and Durango is partially because of the actions carried out by this man," Mr Sanchez said.
Nunez is wanted in the US on drug-trafficking charges. The Mexican government said he could face up to 40 years in prison in Mexico, and it was not immediately clear whether there was a US extradition request for him.