MEXICO CITY (AP) — A court in Mexico sentenced 11 former police officers to 50 years in prison each for the 2021 slayings of 17 migrants and two Mexican citizens, authorities said Tuesday.

The ex-officers were convicted earlier this year of homicide and abuse of authority. A 12th officer was convicted only of abuse of authority and sentenced to 19 years in prison, said Assistant Public Safety Secretary Luis Rodríguez Bucio.

The officers were members of an elite police group in the northern state of Tamaulipas, across the border from Texas.

They had initially argued they were responding to shots fired and believed they were chasing the vehicles of one of the country’s drug cartels, which frequently participate in migrant smuggling.

Police had burned the victims’ bodies in an attempt to cover up the crime. The bodies were found piled in a charred pickup truck in Camargo, across the Rio Grande from Texas, in an area that has been bloodied for years by turf battles between the remnants of the Gulf cartel and the old Zetas cartel.

Most of the dead migrants were from rural, Indigenous farming communities in Guatemala. Relatives said they lost contact with 13 of the migrants as they traveled toward the United States.

The truck holding the bodies had 113 bullet impacts, but authorities were confused by the fact that almost no spent shell casings were found at the scene. It later came out that the state police officers involved in the killings knew their shell casing might give them away, so they apparently picked them up.

The officers were members of the 150-member Special Operations Group, known by its Spanish initials as GOPES, an elite state police unit which, under another name, had previously been implicated in other human rights abuses. The unit has since been disbanded.

So fearsome was the unit’s reputation that the U.S. government, which trained a few of its individual members, sought at the time to distance itself from the force, which it referred to both by its former initials, CAIET, and GOPES.

The U.S. Embassy in Mexico City said in 2021 that three of the 12 officers charged in the migrant massacre “received basic skills and/or first line supervisor training” through a State Department program before they were assigned to the special unit. “The training of these individuals took place in 2016 and 2017 and were fully compliant” with rules on vetting over human rights concerns, the embassy said.

The killings revived memories of the gruesome 2010 massacre of 72 migrants near the town of San Fernando in the same gang-ridden state. But those killings were done by a drug cartel, while the 2021 slayings were carried out by law enforcement.