A jailed suspected member of the Sinaloa Cartel who was to be extradited to the United States was found dead on Dec. 28 at a prison complex in the Mexican state of Oaxaca.

U.S. authorities sought Arturo Díaz Díaz as an operator for fugitive drug lord Joaquín Guzmán Loera, better known by his alias "El Chapo." Authorities told Díaz's attorneys and members of his family that the inmate was believed to have committed suicide, El Diario de Yucatán reported based on unidentified witnesses.

Díaz had been held at a medium-security prison in spite of his suspected connections to the Sinaloa Cartel, one of the most powerful and violent organized crime syndicates involved in wide-ranging drug-trafficking and money-laundering operations. He had been apprehended in October in Mexico City, and local authorities planned to comply with the U.S. extradition request.

In fact, a Mexican court had already authorized Díaz's extradition, which had been requested by  U.S. District Court for the District of Arizona, more than two years ago, El Diario de Yucatán added. American prosecutors accused the man of managing the Sinaloa Cartel's registry of narcotics that were being sent into the U.S. market, as well as of having arranged the logistics of the transport of the illegal drugs.

Following his arrest, Mexican authorities alleged that Díaz worked directly for Adelmo Niebla González, one of Guzmán's closest associates, Proceso reported. Niebla had once been held at a prison complex in the Sinaloa state capital of Culiacán until he escaped through a tunnel in May 2014.

Guzmán himself, meanwhile, made international headlines several times over the last few years due to his surprising capture and subsequent escape.

Mexican authorities had taken the drug lord into custody at a beachfront hotel in Mazatlán, Sinaloa, in February 2014. But the cartel leader, whose exact date of birth is unknown but who is believed to be around 60 years of age, was able to flee a maximum-security prison in July, and police have not been able to apprehend him since.