The man arrested near the U.S.-Mexico border was not linked to the suspected cartel massacre of three women and six children, Mexican officials said Wednesday – as authorities appear to be struggling to narrow down which cartel was responsible for the heinous attack.

Preliminary information indicated the unnamed suspect, who was arrested Tuesday in the border town of Agua Prieta, was not linked to the attack, despite being found with four assault rifles and two hostages bound and gagged in his bulletproof vehicle, public security official Alfonso Durazo said Wednesday.

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Since the massacre on Monday in northern Mexico’s Sonora state, authorities have faced mounting pressure to bring those who carried out the killings to justice. Two separate drug cartels have reportedly been the focus of their investigation: “La Linea” and “Los Jaguares.”

The suspect arrested in the town of Agua Prieta, right across the border from Douglas, Ariz., was not linked to the attacks, Mexican officials said Wednesday.

The suspect arrested in the town of Agua Prieta, right across the border from Douglas, Ariz., was not linked to the attacks, Mexican officials said Wednesday.

The killers were initially believed to be from La Linea, the armed wing of the Juarez drug cartel that was fighting a brutal turf war against a rival faction of the Sinaloa cartel known as the “Salazar.”

However, Cesar Peniche Espejel, Attorney-General of Chihuahua state, told Mexico’s Imagen Radio on Tuesday that he believed the newly-formed Los Jaguares cartel, an offshoot of the Sinaloa cartel, may be behind the slaughter.

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He also mentioned La Linea and the “Jalisco Nueva Generacion,” a cartel also known to operate in those areas, but couldn’t confirm whether any of the groups were involved.

“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.”

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With the territorial disputes in Sonora and Chihuahua, Mexican officials have said the attackers may have mistaken the families’ large SUVs for those of a rival gang.

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“Those who attacked the occupants (of the vehicles), they let the children go, so that we can deduce that it was not a targeted attack” against the families, Army chief of staff Gen. Homero Mendoza said.

However, Daniel Lebaron, a cousin of Rhonita Maria Miller, a mother who was shot and burned to death along with four of her children, disputed that claim, telling told Fox News on Wednesday that it appeared to be a “direct attack.”

Relatives grieved Wednesday next to the burnt wreckage of a vehicle where some of their relatives died earlier this week. 

Relatives grieved Wednesday next to the burnt wreckage of a vehicle where some of their relatives died earlier this week.  (Reuters)

“We thought it might have been mistaken identity,” he told “America’s Newsroom” anchor Bill Hemmer via phone. “Now we've had quite a bit of evidence that once the attack began, they continued it, knowing that there were women and children in the vehicles. So, as far as why it happened — we're not sure yet.”

“But it definitely was not crossfire between cartels,” he added. “This was a direct attack, apparently, from the one cartel.”

Mexico's President Andrews Manuel Lopez Obrador has faced mounting criticism for his government's policy of using “hugs, not bullets” with regards to the cartel.

On Wednesday, he reiterated that violence was not the answer or appropriate response to the growing deaths at the hands of the cartels.

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On Thursday, hundreds of mourners from the U.S. spent the night in a remote farming community in northern Mexico ahead of scheduled funerals for some of the victims, the Salt Lake Tribune reported.

Most of the victims lived in La Mora, a Mormon offshoot community about 70 miles south of Douglas, Ariz.

Fox News' Dom Calicchio and The Associated Press contributed to this report.