Two of four Americans kidnapped by gunmen on Friday just after they drove into northeastern Mexico have been found dead, US and Mexican officials said on Tuesday, in a grim reminder of the lawlessness plaguing parts of the border region.

The survivors and the two bodies were discovered by Mexican security forces on Tuesday morning in a wood cabin southeast of the border city of Matamoros, said Americo Villarreal, governor of Tamaulipas, the state the four crossed into from Texas.

Authorities were still investigating how the two Americans died, and one Mexican official said the most likely explanation for the group’s abduction was a case of mistaken identity.

One of the two surviving Americans suffered a gunshot wound to his leg that was not life-threatening, while the other, a woman, was not injured, Villarreal told a news conference.

A Mexican woman, 33, also died during the kidnapping ordeal, apparently from a stray bullet, he said.

A 24-year-old man guarding them at the cabin was arrested at the scene. Before they were found, the four had been moved to a succession of locations in the area, including a local clinic in a bid to throw law enforcement off the trail, Villarreal said.

“We’re very sorry to have this happen in our country and we send our condolences to the families of the victims, their friends, to the people of the United States,” President Andres Manuel Lopez Obrador told an earlier news conference.

Mexican officials on Tuesday morning handed the survivors to US officials at the border, and the two bodies were to follow in the next few hours, Villarreal said. The US State Department confirmed two Americans had returned to the United States.

Mexican officials pledged to work with the US to find the perpetrators, but the incident threw a harsh spotlight on gang violence in Mexico and sparked angry reactions from some US lawmakers critical of Mexican efforts to fight crime.

The four Americans were in a white minivan when they entered Matamoros on Friday. Gunmen fired at them soon afterwards and then forced them into another vehicle, officials said.

A video circulating on social media purportedly of the kidnapping showed a woman being walked towards a white pickup truck by a group of men with body armor and guns. She was forced into the back before the men dragged in two prone figures.

Tamaulipas is one of Mexico’s most gang-ravaged states and has long been plagued by the kidnapping of migrants.

ABC News on Monday named the four Americans as Shaeed Woodard, Zindell Brown, Latavia McGee and Eric James Williams. A Tamaulipas official identified the last two as the survivors.

Williams was receiving treatment in hospital in Brownsville, Texas, across the border from Matamoros, the official said.

MILITARY THREAT

US Republicans, in particular, have been pushing for the US government to take a tougher line on organized crime south of the border amid rising overdose deaths caused by fentanyl, a synthetic opioid trafficked by Mexican cartels.

Republican Senator Lindsey Graham on Monday said it was time to “put Mexico on notice,” advocated introducing legislation to classify some Mexican drug cartels as “foreign terrorist groups”, and set the stage to use military force if necessary.

“I would tell the Mexican government if you don’t clean up your act, we’re going to clean it up for you,” he told Fox News.

White House spokesman John Kirby condemned the incident in Tamaulipas. “Attacks on US citizens are unacceptable, no matter where,” he told a news briefing.

Tamaulipas Attorney General Irving Barrios told the conference with Villarreal that the Gulf Cartel was known to operate in the area but stopped short of explicitly blaming it.

Barrios said the Americans were likely mistaken for somebody else when abducted but noted authorities were still pursuing several lines of investigation.

Tamaulipas officials said McGee was traveling with the group to Mexico to get cosmetic surgery.

Mexican President Lopez Obrador vowed to bring the killers to justice. But he lashed out at what he cast as “tabloid” coverage of the incident and accused the media of not giving the same attention to killings of Mexicans in the United States.