U.S. authorities handed over Mexican drug lord Hector “El Guero” Palma to Mexico Wednesday where he was immediately arrested on homicide charges, Mexican officials said.

Palma, who is reportedly one of Mexico’s most notorious drug lords, had served nine of his 16-year jail term in a U.S. prison and was to be released early for good behavior. A former accomplice of Joaquin “El Chapo” Guzman, Palma has been transferred to a maximum-security lockup in Mexico until he goes to trial for two murders.

The Mexican federal prosecutor’s office confirmed in a statement that the U.S. handed over Palma at a border gate in Matamoros, Mexico, across Rio Grande from Texas on Wednesday, the Associated Press reported.

Palma, the statement said, was arrested at the border for “his probable responsibility” for two murders.

Attorney General Arely Gomez of Mexico reportedly said her office was checking if there were any pending cases against Palma. “We are in the process of carrying out an exhaustive review, checking all the prosecutors' offices,” she said.

Hector 'El Guero' Palma Drug lord Hector 'El Guero' Palma is escorted by U.S. authorities before being turned over to Mexican authorities at the Puente Nuevo international bridge in Brownsville, Texas, opposite the Mexican border city of Matamoros, June 15, 2016. Photo: REUTERS/STRINGER

The 55-year-old drug lord was one of the founders of the Sinaloa cartel, of which Guzman was the leader. The cartel specialized in trafficking cocaine from Colombia to the United States. Palma was arrested in June 1995 when a small plane ferrying him to a party in the northern Mexican city of Guadalajara crashed. Palma and Guzman were co-inmates at the Puente Grande prison in Jalisco, Mexico, in 2001.

Palma was transported to the Altiplano prison, outside Mexico City, which happens to be the same prison Guzman escaped from in 2015.