A San Diego man detained by the Border Patrol after being caught carrying three pounds of marijuana died in a holding cell Christmas Eve. Steven Keith, 58, becomes the 41st person to die in US domestic drug law enforcement operations so far this year.

According to the Associated Press, Keith was stopped at a Border Patrol checkpoint on Interstate 8 in Southern California, and authorities found the marijuana, along with unspecified drug paraphernalia and traces of methamphetamine in his vehicle.

He was then arrested and placed in a holding cell, where he collapsed shortly thereafter. Paramedics were unable to revive him.

The Border Patrol said it is cooperating with an investigation being undertaken by the San Diego County Medical Examiner's Office, but as NBC San Diego reported, local human rights activists are pointing out that Keith's is only the latest death in Border Patrol custody.

"Since 2010, we have had more than 20 individuals who have died while in Border Patrol custody. We don't have any answers as to what happened in any of those cases. Those are all pending investigation or investigations that have never even started," said Andrea Guerrero, executive director of Alliance San Diego. "We haven't seen any outcomes on any of the other cases," Guerrero said. "And so, it should be concerning to the general public and for the family that this is yet another case. We're just mounting up cases is all we're doing. We're not getting any answers."