After the four US citizens who were kidnapped by Mexican drug cartels were located in a shed near the city of Matamoros, a criminal drug cartel seems to have assumed responsibility in an unanticipated way over the case.
A few days after the Americans - two dead, two alive - were returned to the US, authorities found five men beaten and tied up inside a pick-up truck.
Near them was a handwritten letter, apologising in Spanish to the families of the victims, including a Mexican woman who was killed by a stray bullet, and to the residents of Tamaulipas state.
