The head of Rolando Flores, the chief investigator in Ciudad Miguel Aleman, was stuffed in a suitcase, ABC News reported.
Flores had been investigating the disappearance of David Hartley of Texas, who has not been seen since Sept. 30 after being shot on the Mexican side of Falcon Lake while riding a personal watercraft with his wife Tiffany.
Tiffany Hartley has told police her husband was shot by pirates. His family has criticized Mexican authorities for not pursuing the investigation into his disappearance aggressively enough.
ABC said Texas state Rep. Aaron Pena tweeted Tuesday he had confirmed through Zapata County Sheriff Sigifredo Gonzalez that Flores had been decapitated.