A Mexican police chief investigating the disappearance of a US man on a lake bordering Mexico earlier this month has been found dead.
Commander Rolando Flores was working on the case of tourist David Hartley, whose wife reported that he had been shot by pirates on Falcon Lake.
Texas Governor Rick Perry said Mr Flores's death was a message from a gang to "stay out of their territory".
However, Mexican officials have said Mr Flores was working on multiple cases.
Mr Perry told the Associated Press news agency that he thought the killing was an "attempt to intimidate law enforcement, no matter who they are or where they are".
According to Zapata County Sheriff Sigifredo Gonzalez, the head of the decapitated police commander was found on Tuesday in a suitcase outside a Mexican army base, AP reports.
Mr Hartley's wife, Tiffany, said she and her husband were crossing the lake on jet skis when they were attacked and shot at by pirates from a speedboat.
Her husband was shot and fell into the water and she was forced to flee as the men continued to fire, she added.
The US State Department has issued repeated travel warnings to Americans traveling to or living in Mexico, particularly in relation to the area just south of the border.