Police in Mexico have arrested a suspected lieutenant of a drug cartel for the murders of more than 350 people.
Mario Nunez, 39, is accused of being the second highest-ranking member of the Sinaloa gang, allegedly run by Mexico's most wanted man, Joaquin Guzman.
Nunez, a former police officer, was arrested in the city of Ciudad Juarez, which borders El Paso, Texas.
Nunez, also known as M-10, is suspected of being behind the 2011 murders of 350 people whose bodies were discovered in 23 mass graves in the northern state of Durango. The Mexican government claim the murders were a result of a feud with another Mexican drug chieftain.
National security spokesman Eduardo Sanchez said: "[Nunez] is related to, and believed to be responsible for, the murder of more than 350 people recovered from 23 hidden mass graves.
"Much of the violence seen in the states of Chihuahua and Durango is partially because of the actions carried out by this man."
Nunez could face up to 40 years in jail. He is also wanted in the US on drug-trafficking charges. It is not known if the US has requested him to be extradited.
Nunez began working with the Juarez cartel before joining the rival Sinaloa, widely regarded as one of the most powerful drug organisations in Mexico.
US court documents say Guzman, known as El Chapo, hired Nunez and gave him the job of taking the smuggling corridors from the US to Mexico from the Juarez cartel.
Nunez is suspected of ordering gangs of hitmen to carry out killings which involved mutilations and decapitations.