A group of FBI agents and support staff crossed into Mexico Sunday, November 10, to join the investigation into the Mormon family murders that left nine dual citizen women and children dead earlier this month.

A team of FBI personnel made their way to Bavispe, Sonora, approximately 90 miles south of the U.S. border. The area around Bavispe is where a group of cartel gunmen ambushed, murdered, and incinerated six children and three women from a nearby Mormon community. Six other children from the same family were injured. All had dual U.S. and Mexican citizenship.

The government of Mexico invited the FBI agents late last week. Secretariat of Foreign Relations Marcelo Ebrard said that the FBI would “accompany” investigative personnel from the federal prosecutor’s office. Mexican federal investigators are handling the November 4 case.

Secretariat Ebrard said the FBI agents would be unarmed with a limited in scope of investigation. He further advised that authorities from the border state of Sonora already have several suspects in custody, but did not elaborate further.

A spokesperson for the FBI confirmed they would be “providing assistance” under Mexico City’s invitation. It is unknown how long the agents and staff will remain in country for this particular case.

Robert Arce is a retired Phoenix Police detective with extensive experience working Mexican organized crime and street gangs. Arce completed work assignments in the Balkans, Iraq, Haiti, and recently completed a three-year tour in Monterrey, Mexico, for the U.S. Department of State, International Narcotics and Law Enforcement Program.