Authorities in Mexico have arrested a municipal police chief there for his alleged role in the killing of nine women and children in early November, Reuters reported.

The victims were all U.S. citizens who have lived in a fundamentalist Mormon community in the border-area between the U.S. and Mexico for decades. Three mothers and six children were traveling in a caravan of three cars near La Mora, Mexico, when assailants opened fire on the vehicles.

Reuters reports that Fidel Alejandro Villegas, who is the police chief of Janos in the neighboring state of Chihuahua, was arrested for his alleged involvement in the crime. While the news organization says he is suspected of having ties to organized crime, it doesn’t say how he is allegedly linked to the slayings.

Police have said the victims were killed after being swept up in a fight between two feuding drug cartels, and the killings prompted comments from U.S. President Donald Trump, who said the U.S. would help “in cleaning out” the cartels, as well as from those who want polygamy legalized in the U.S.

“If polygamy were legalized,” said Brooke Richey, a 23-year-old Utahn with family living in Mexican Mormon communities, “they probably would come back to the U.S. It just seems like they’re in such a vulnerable place.”