The Gulf cartel apologized Thursday after two American citizens were killed during an armed abduction last week in Mexico.
The cartel condemned the violence in a letter obtained by The Associated Press and said they had turned over members who were involved. A senior law enforcement official told NBC News that U.S. authorities believe the letter is legitimate.
"The Gulf Cartel Grupo Escorpiones strongly condemns the events of Friday, March 3 in which unfortunately an innocent working mother died and four American citizens were kidnapped, of which two died," a translation of the letter states. "For this reason, we have decided to hand over those involved and directly responsible for the events who at all times acted under their own determination and indiscipline and against the rules in which the CDG has always operated."
Four Americans were shot at and kidnapped after driving into Matamoros, Mexico, just south of Brownsville, Texas, for a medical procedure. Video showed a gunman dragging people into a white pickup, a law enforcement source with knowledge of the matter previously said.
Tamaulipas state Gov. Américo Villarreal said at a news conference that a woman, identified by family as LaTavia Washington McGee, and a man, Eric Williams, survived the kidnapping.
Both were taken to a clinic for medical treatment and returned to the U.S. by an international bridge between Matamoros and Brownsville.
McGee's mother said she had spoken to her daughter, and Williams' wife said he had been shot in the leg but was back in the U.S.
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Zalandria Brown of Florence, South Carolina, told The Associated Press that her younger brother, Zindell, was among the four victims. Aliyah McCleod, McGee's cousin, identified another member of the group as Shaeed Woodard.
McCleod said the group is from South Carolina and had been traveling in a rental vehicle with North Carolina license plates when it entered Matamoros. Williams' wife described the group as childhood friends.
A fifth person was along for the trip from South Carolina. That traveler got out just before the group reached the border because that person didn't have the documentation needed to cross into Mexico, a law enforcement official told NBC News on Wednesday.
That fifth person could be seen riding with the group, in video taken by Williams.
A law enforcement official with knowledge of the matter said a woman in the group had been seeking a cosmetic medical procedure. The official said cartel gunmen targeted the group in a case of mistaken identity.
In its letter, the Gulf Cartel said it respects the "life, tranquility and integrity of the innocent" and apologized to "the society of Matamoros ... the affected American individuals, and families."
"In addition the CDG asks society to remain calm because we are committed to ensure that these errors caused by indiscipline aren't repeated. The guilty parties will pay, regardless of who they are," the letter reads.
A 24-year-old man from Tamaulipas state, identified only as Jose N, "was found guarding the victims" and was arrested, Villarreal said. It's not clear what charges he faces.
The State Department issued a "Do Not Travel" for Tamaulipas, noting organized crimes including gun battles, murder and kidnapping are common along the northern and in Ciudad Victoria.