Mexico City — Mexican authorities have made an arrest they believe may be connected to the ambush killings of nine Americans in northern Mexico earlier this week. The state prosecutor’s office in Sonora state, where the killings occurred, said in a statement posted to social media that agents detained a heavily-armed man close to where the attacks took place, and that “the possibility” that he might have participated in the massacre was “being analyzed.”

Sources have told CBS News the victims may have been targeted by a drug cartel. Some of the survivors remained hospitalized Wednesday morning with gunshot wounds.

Three women and six children were killed, including eight-month-old twins. They all belonged to a break-away group once associated with the Mormon Church.

As CBS News correspondent Mark Strassman reports, the Sonora prosecutor’s office said the person arrested was found in a vehicle with two other people who were bound and gagged. Those unidentified individuals were rescued, and four assault-style weapons, spent magazines and high-caliber ammunition, were seized. Two vehicles were seized separately, including one said to have been armored.

Deliberately targeted?

Mexican officials said the family might have been mistakenly caught in a battle between two rival gangs, a theory also put forth by President Donald Trump in a tweet early Tuesday. But CBS News sources said the leading scenario is that the extended family was deliberately targeted.

Lending credibility to that theory is the fact that the ambush was drawn out over time, and miles, and continued after witnesses say one woman identified herself to the gunmen.

Taylor Langford is the nephew of one of the women killed in the brazen ambush. He and other family members also wonder if the attack was intentional.

“Three vehicles with women and children in broad daylight. There was no mistaken identity,” he told CBS News on Tuesday. “I felt this was in broad daylight and … no one could have done that not knowing what they were doing.”

Women and kids gunned down

Among the dead are 30-year-old Rhonita Miller and her children, 12-year-old Howard Junior, 10-year-old Krystal and eight-month-old twins Titus and Tiana. The SUV they were traveling in was hit with so many rounds that the gas tank exploded. Video showed the charred remains of the vehicle by the side of the road in a remote desert region, about 100 miles from the U.S. border.

Two more SUVs filled with family members were fired on about 10 miles further down the same road. It was an overwhelming onslaught; investigators found more than 200 shell casings, mostly from assault weapons, at the scene.

That’s where Dawna Langford and her children, 11-year-old Trevor and two-year-old Rogan were killed.

Just yards away, 29-year-old Christina Langford Johnson hid her baby on the floorboards of the back seat. Officials say she got out with her hands up, but was shot and killed. Her baby, seven-month-old Faith, was found 11 hours later unharmed.

Amid the chaos, 13-year-old Devin Langford was able to hide six of his injured brothers and sisters in nearby brush, covering them with branches before walking 14 miles to find help.

A relative has said that when he took too long to return, his 9-year-old sister Mckenzie left her siblings behind and walked for hours in the dark before she was found.

Some of the surviving children were airlifted from the scene and brought to a hospital in Tucson, Arizona, for treatment.

Cody, 8, was shot in the jaw and leg. Fourteen-year-old Kylie was shot in the foot and four-year-old Xander was shot in the back. Brixton, just eight months old, sustained a gunshot wound in the chest.

Mexico declines help to “wage war”

On Twitter, President Trump offered condolences and military aid to Mexico.

“This is the time for Mexico, with the help of the United States, to wage WAR on the drug cartels,” Mr. Trump wrote.

Mexico’s President Andrés Manuel Lopez Obrador respectfully declined, saying it was an issue for his country to address independently.

Drug-related violence is nothing new in Mexico, but this attack has shown cartel gunmen becoming increasingly unconcerned about children being killed in the crossfire.