Texas legislator Aaron Peña posted a horrible notice to his Twitter account yesterday: A Mexican investigator working the case of murdered Colorado native David Hartley "was decapitated, his head delivered to MX military."

Indeed, as myriad news agencies have confirmed, Tamaulipas police Commander Rolando Flores, who was looking into the disappearance/alleged shooting death of Hartley on the Mexico-Texas border, was murdered in the border city of Ciudad Miguel Aleman. A spokesman for the Tamaulipas state prosecutor's office says Flores "unfortunately was killed," and authorities "don't know how or why" (via 9News).

Meanwhile, after telling news agencies of possible suspects in Hartley's case, Mexican officials are backing down from the investigation, according to CBS4. David Hartley's father, Dennis Hartley of Milliken, says working with Mexican officials has been frustrating: "You hear information one day of things going on; the next day, or hours later on that same day, it's not going on."

As of September 25, four Mexican mayors had been slain in violence attributed to cartels, including one in the state of Tamaulipas (via the Los Angeles Times). The particularly troubled state also saw the assassination of a gubernatorial candidate back in June (via The New York Times).

Vanessa Martinez contributed to this post.