MATAMOROS, Mexico - Suspected drug cartel members on Thursday handed over five henchmen purportedly responsible for the abduction of four Americans in the border city of Matamoros as a would-be apology, according to media and a source familiar with the investigation.

Mexican officials found the Americans in a wooden shack on the outskirts of Matamoros on Tuesday after a tip-off. Two of them and a female Mexican bystander were found dead.

Mexican officials gave the bodies of the two dead men, identified as Mr Shaeed Woodard and Mr Zindell Brown, to US officials in Matamoros on Thursday afternoon, which were taken across the border into the US, a Reuters witness said. Their two surviving companions returned to the US earlier this week.

Gunmen had opened fire on the United States citizens shortly after their arrival in Matamoros last Friday before bundling them into another vehicle that fled the scene.

Mexican authorities have suggested the attack was the result of a “mix-up” rather than a targeted one.

The Americans had visited Mexico as one of them was planning to have cosmetic surgery, according to a Mexican official.

An internal government document seen by Reuters indicated that a faction of Mexico’s Gulf Cartel was likely responsible for the kidnappings, and that the gunmen may have believed that the Americans were encroaching on the gang’s turf.

On Thursday, Mexican newspapers and social media published photos of a letter attributed to a different faction of the cartel in which it apologised for the events in Matamoros, and said it was handing over five men who were involved in the kidnappings.

The letter for Mexican authorities was left alongside five men, who had their hands bound, the photos showed. The Mexican source familiar with the investigation confirmed the handover, but expressed scepticism that the five were the ones responsible for the attack.

The attorney general’s office of Tamaulipas, the state where Matamoros lies, declined to comment on the reports.

Separately, the state attorney general’s office said its investigation indicated that the Americans were taken by their kidnappers to a clinic where they were given medical attention. REUTERS, AFP