A man arrested Tuesday in the Mexican border city of Agua Prieta with a cache of weapons was not involved in the killings of nine U.S. citizens, Mexican officials say, as pressure mounted on the government to make an arrest.

Alfonso Durazo, a public security official, said Wednesday that preliminary information indicates that the suspect detained Tuesday is not linked to the attack, The Associated Press reported. NBC News was not immediately able to independently verify the AP report.

Ronita Miller, her twins Titus and Tiana, and Langford Johnson and her son Trevor were all killed in the attack. Courtesy Kendra Miller

Earlier, criminal investigators in Mexico had said the suspect — who was found with multiple assault weapons on him and two hostages in his captivity — may have participated in Monday's brutal highway ambush, which killed three women and six children, including two infants.

The development brings the investigation back to square one, as officials and victims' relatives on both sides of the border called for a speedy arrest in the case.

The attack happened on a highway in the northern Mexican border state of Sonora as several families were traveling in a convoy of large SUVs that investigators believe drug cartels may have mistaken for those of rival gangs.

Relatives of the victims described a harrowing scene, with bullets flying at mothers and their children and a car bursting into flames when its gas tank was apparently shot. Eight children ranging from 7 months old to early teens survived; five are currently hospitalized in Phoenix, including some with serious injuries.

On Thursday, the first funerals were held for some of the victims.

Mourners earlier in the week arrived in the municipality of Bavispe, where the funerals are being held, in dozens of SUV-style vehicles and pickup trucks escorted by the Mexican National Guard, Reuters reported.

The coffins of Rhonita Maria Miller and her four children, members of the Mexican-American Mormon community killed by unknown assailants, are pictured before their funeral in La Mora, Sonora state, Mexico on Nov. 7, 2019. Jose Luis Gonzalez / Reuters

"We came prepared to sleep on the floor, in tents. Whatever is needed to support the families who died in this terrorist act," Alex LeBaron, a former congressman and cousin of one of the women, Rhonita Miller, said, adding that mourners had come from across the United States and Mexico, according to Reuters.

Miller is set to be buried on Friday, Reuters reported. On Thursday, funerals were held for Dawna Ray Langford, 43, and her children, Trevor Harvey Langford, 11, and Rogan Jay Langford, 2.

Mexico's president has invited U.S. authorities to aid in the investigation into who is responsible for the victims' deaths, and President Donald Trump has said in tweets that the United States is "ready, willing and able" to help Mexico "in cleaning out these monsters."

The victims of the attack lived in Mexico and all belonged to a Mormon offshoot group. Some family members have disputed Mexican authorities' account of the killings being a case of mistaken identity, arguing that cartel members know everyone in the area and would be unlikely to make such an error.