Two of the four Americans kidnapped in Mexico have been found dead, while the other two were rescued alive, officials announced Tuesday.
The survivors -- Eric James Williams and Latavia "Tay" McGee -- have returned to the U.S., their families said.
The four Americans -- Williams, McGee, Zindell Brown and McGee's cousin Shaeed Woodard -- arrived Friday morning in Matamoros, Mexico, which is in the northeastern state of Tamaulipas just south of Brownsville, Texas.
"Shortly after crossing into Mexico, unidentified gunmen fired upon the passengers in the vehicle," the U.S. Embassy in Mexico City said. The Americans had been traveling in a white minivan.
"The gunmen herded the four U.S. citizens into another vehicle and fled," the embassy said.
The Americans were not directly targeted, Attorney General of Tamaulipas, Irving Barrios, said at a news conference.
It "seems to be that it was a misunderstanding," Barrios said.
Mexican investigators believe the kidnappers may have wrongly believed the Americans were rival human traffickers, a source close to the investigation told ABC News.
The two survivors were found Tuesday morning in a wooden house in the Lagunona area, outside of Matamoros, Mexican officials said at a news conference. One of the deceased was also found inside the house, and the second was found outside it, a source close to the investigation told ABC News.
Williams had a gunshot wound to his leg, said the governor of Tamaulipas, Américo Villarreal.
During the three days they were held, the Americans were transferred to various places, including a clinic, in order to create confusion and avoid rescue efforts, Villarreal said.
One person has been arrested. The 24-year-old suspect was in charge of looking after the victims inside the house where they were found, Mexican officials said.
One of the survivors, McGee, is a mother of five who traveled from South Carolina to Mexico for a cosmetic medical procedure.
Her mother, Barbara Burgess, told ABC News she "had to hold my heart" when the FBI came to her home on Tuesday with the news her daughter was alive.
McGee spoke to her mother from a Texas hospital on Tuesday and told her mother she had no major injuries, Burgess said.
Williams, the second survivor, called his wife, Michele Williams, as he was being transported to a Texas hospital, she told ABC News.
"It was just tears of joy," she said.
Michele Williams said the FBI told her that her husband had been shot twice in one leg and once in the other. He underwent surgery in Texas for the wounds, she said.
MORE: 4 US citizens kidnapped in Mexico identifiedThe surviving victims were transported to the Port of Entry in Brownsville, where they are receiving medical care at a local hospital, the FBI said in a statement Tuesday. One of the victims "sustained serious bodily injuries during the attack," the FBI said.
"This is still an ongoing criminal investigation," the FBI said, adding that it is working with federal and international partners "to determine the facts of what happened and to hold those responsible for this horrific and violent attack accountable for their crimes."
The bodies of the two deceased Americans will be transferred to the U.S. on Tuesday, Mexican officials said. The State Department is "in the process" of repatriating the two deceased victims, spokesperson Ned Price said Tuesday afternoon.
Autopsies will be conducted on the two victims who were killed, a source close to the investigation told ABC News.
National Security Council spokesperson John Kirby told reporters Tuesday, "We offer our deepest condolences to the friends and families of those who were killed in these attacks."
Price said, "We thank our Mexican and U.S. law enforcement partners for their efforts to find these innocent victims and the task forward is to ensure that justice is done."
President Joe Biden has "been kept updated" on the situation, White House press secretary Karine Jean-Pierre said Tuesday, adding that U.S. officials are in touch with the families.
Jean-Pierre called attacks on U.S. citizens "unacceptable."
U.S. Attorney General Merrick Garland said in a statement Tuesday that the Department of Justice will do "everything in our power" to hold those responsible for the attack to account.
ABC News' Ellie Kaufman, Matt Rivers, Anne Laurent, Shannon Crawford, Dan Carranza and Luke Barr contributed to this report.