A suspect was arrested Wednesday in connection with the murder of nine members of a Mormon family in Mexico near the U.S. border.

The three women and six children from the LeBaron family, all dual U.S.-Mexico citizens, were gunned down by suspected drug cartel members on Tuesday in the state of Chihuahua.

The Ministerial Agency for Criminal Investigations (AMIC) of Mexico announced it had found the suspect traveling near the Arizona border with two bound-and-gagged hostages. The suspect also was in possession of several rifles and high-caliber ammunition, and had a bulletproof SUV.

U.S. and Mexican authorities offered conflicting accounts of which cartel was responsible for the killings. Cesar Peniche Espejel, the Attorney General for Chihuahua, said he believes an offshoot of the notorious Sinaloa cartel is responsible, while U.S. authorities are looking into a different cartel called La Línea.

“These very cartels of Sinaloa, after the arrest of Guzman ‘El Chapo’ have suffered fragmentations,” Peniche Espejel said. “They have been growing near the border with the United States and are heavily involved in trafficking of immigrants into the United States and drug-trafficking.”

The FBI announced it was ready to assist Mexico investigate the killings, although as of Wednesday morning there was no response from Mexican authorities.

Former Mexican foreign minister Jorge Castañeda told CNN on Tuesday the family has a history of “friction” with cartel members.

“They had stood up to the drug cartels and they did have certain frictions either with the cartels or with neighboring communities over water rights,” Castañeda said. “Apparently the woman who was driving in the first car that was attacked was an activist. She was someone who was very active in her community, defending her family, her fellow members of the community against cartels, on the issue of water rights.”

The LeBaron family settled in Chihuahua in the 1940s. They speak English among themselves, and worship at a church decorated with quotes from George Washington and Benjamin Franklin.

President Trump on Tuesday offered to help Mexico to fight drug cartels in the country.

“If Mexico needs or requests help in cleaning out these monsters, the United States stands ready, willing & able to get involved and do the job quickly and effectively,” Trump wrote on Twitter.

Mexican President Andrés Manuel López Obrador thanked Trump but declined his offer, saying “The worst thing you can have is war.”