SAN DIEGO — A former law enforcement official in Mexico who worked closely with US authorities on cross-border criminal investigations was sentenced Monday to more than eight years in prison for aiding Mexican drug traffickers.

Jesus Quinonez, 41, told a judge that what began as a well-intentioned relationship with an informant led him to make mistakes.

He faced a maximum possible sentence of life in prison for racketeering conspiracy, but prosecutors sought only eight years and one month as part of a plea agreement reached in May, as his trial was set to begin.

Quinonez was the international liaison for Baja California’s attorney general, Rommel Moreno, serving as his primary contact with US state and local law enforcement agencies in an area that includes the border cities of Tijuana and Mexicali.

As part of the plea agreement, Quinonez admitted that he agreed to help smuggle $13 million into Mexico with a group headed by Fernando Sanchez Arellano, a nephew of the Arellano Felix brothers. He was working with a Sanchez Arellano lieutenant, Jose Alfredo Najera Gil, but the smuggling operation was never consummated.

Quinonez also admitted sharing information with a reputed lieutenant for Sanchez Arellano, Jose Alfredo Najera Gil, about the investigation of a double homicide in Tijuana in March 2010.

The killings were committed by the Sanchez Arellano gang, according to the plea agreement.

The Arellano Felix cartel was once one of the world’s most powerful drug cartels, but its power began to erode in 2002 when its leaders began getting killed or captured.