© Herika Martinez/Agence France-Presse - Getty ImagesOne of the three vehicles that carried members of a family that was attacked in Sonora.
MEXICO CITY - A conflict between two criminal groups fighting for control of a region in northern Mexico is a focus of the authorities in their investigation into the massacre of nine members of a Mormon family, officials said Wednesday.
Gen. Homero Mendoza Ruiz, Mexico's chief of staff for national defense, said that before the family was attacked on Monday, the groups had a shootout in the town of Agua Prieta, on the border with the United States. At least one person died and another was wounded.
The authorities identified the groups as Los Salazar, based in the state of Sonora, and La Línea, based in the neighboring state of Chihuahua. After the gang shootout Monday morning, they said, La Línea dispatched gunmen to a region that straddles the two states to try to prevent their rivals from entering Chihuahua.
The attack on the Mormons as they drove through Sonora, toward the border with Chihuahua, General Mendoza said, is being attributed to this clash between the rival gangs. It remained unclear, however, whether the family was somehow involved in the rivalry or whether the attack was a case of mistaken identity.
The SUV model that two of the victims were driving, a Suburban, is commonly used in the area by criminal gangs, the general said. He added that investigators believed that the children in one of the Suburbans were allowed to flee, contributing to the hypothesis that the attack was not directed at the family.
The family members, all women and children who were dual American and Mexican citizens, were ambushed while driving in three sport utility vehicles in a rural area of Sonora where Mormon groups that splintered from the main United States church began settling in the early 20th century.
Six children and three women were killed.
The attack terrified communities that had learned to coexist with violence in the remote, rural area, said a human-rights activist who lives and works in the region and who did not give his name out of fear of reprisal from the gangs.
The criminals showed "no mercy even with children and babies," he said. "This only adds to the fear that we already felt, which is now maximized."
At a news conference on Wednesday, Mexican government officials offered few new details about the ambush and its motivations, saying that the investigation was continuing. But they determined that the ammunition used in the attack were .223 caliber cartridges manufactured in the United States by Remington and associated with AR-15 and M16 rifles.
Some 200,000 American guns cross the border into Mexico illegally each year, according to some estimates, landing in the hands of the criminal organizations that fight to control the multibillion drug trade to the United States and helping fuel much of the violence overwhelming Mexico. Mexico has been lobbying the United States for more than a decade to stop the flow.
Marcelo Ebrard, Mexico's foreign minister, also said that because the victims were from families that have dual nationality and move frequently between the two countries, Mexican officials would provide their American counterparts with full access to their files as the investigation progressed and would seek the collaboration of United States law enforcement, including the F.B.I., if necessary. © Bryan Denton for The New York TimesA remote stretch of land near Agua Prieta, where rival gangs are said to have had a shootout.
Officials also provided some clarification about the timeline of events on Monday.
General Mendoza said the ambush began with an attack at about 9:40 a.m. on a Tahoe sport utility vehicle that was traveling well behind the other two vehicles and carrying one woman and four children. The Tahoe appeared to have caught fire from the impact of the bullets, he said, and all five passengers were killed.
The second attack, on the two Suburban SUVs that were traveling together, occurred at about 11 a.m., some 11 miles farther along the road. One of the vehicles carried six children, two of whom were killed, and one woman, who was also killed. The other four children escaped.
The other Suburban carried a woman, who was killed, and four children, all of whom managed to escape.
On Tuesday, President Trump wrote in a tweet that this is "time for Mexico, with the help of the United States, to wage WAR on the drug cartels and wipe them off the face of the earth."
Since then, American senators from both parties have criticized Mexico's failure to control the violence and called for its government to step up its fight against the criminal organizations that control swaths of the country and fuel its record-high homicide rate.
"This is what happens when Mexico's politicians look the other way and let drug cartels bribe their way to power," Senator Ben Sasse said in a statement on Tuesday. "Enough. Mexico's president hasn't taken the threat seriously."
But on Wednesday, President Andrés Manuel López Obrador of Mexico defended his security strategy, which has focused on combating the poverty he sees as the root of violence.
"It hurts a lot," Mr. López Obrador said of the attack. "But are we going to want to solve the problem in the same way? Declaring war? That, in the case of our country, has been shown not to work. That was a failure, that caused more violence, acting like this."
It remained unclear what the criminal organizations might have been fighting over, analysts said, though control of lucrative drug trafficking routes was a possibility.
In recent years, La Línea has been active in the mountainous regions of southern Chihuahua state and in the northwest section of the state, analysts said, and has diversified into a wide range of criminal enterprises, including drug trafficking, extortion and kidnapping
Across the state border, in neighboring Sonora, Los Salazar has operated mostly in the southern part of the state and has been associated with what Alejandro Hope, a security analyst in Mexico City, called "a significant rise in violence in the past two years." The group has also been a regional ally of the Sinaloa Cartel.
Mr. Hope said that a significant transit route for illegal drugs runs through the area of Agua Prieta, the border town where Monday's clash took place.
But analysts also pointed out that a history of tension between the Mormon communities and the criminal organizations they have spoken out against also allows for the possibility that the families were targeted.
"These are pretty brutal groups," said Tony Payan of Rice University's Baker Institute for Public Policy. "They would not stop at killing children."
Elisabeth Malkin and Paulina Villegas contributed reporting.