The severed head of a Mexican investigator looking into the disappearance of an American has been delivered to authorities in Mexico, the sheriff on the Texas side of the border told NBC News on Tuesday.
Zapata County Sheriff Sigifredo Gonzalez is spearheading the investigation on the U.S. side. David Hartley vanished on Sept. 30 while on Jet Skis with his wife on Falcon Lake, which stretches into Mexico.
A spokesman for the prosecutor's office in the Mexican state of Tamaulipas confirmed that Commander Rolando Flores, the head of state investigators in the border city of Ciudad Miguel Aleman, had been killed.
Flores was investigating the disappearance of Hartley, but the prosecutor's spokesman said the death was unrelated.
Still, Flores last weekend had delivered information about two alleged Mexican gang members to KRGV TV in Texas as part of its investigation into Hartley's disappearance.
And U.S. authorities have said threats of violence from Mexican drug gangs who control much of the area has hampered the search for Hartley's body.
Texas Gov. Rick Perry said Tuesday that backing down in the face of threats from Mexican drug cartels and gangsters was "the worst thing we can do."
Perry told The Associated Press that the response on both sides of the border should be to increase "the numbers of law enforcement and military."
Perry has been pressuring Mexico to step up the search for David Hartley. Hartley's wife, Tiffany, says she and her husband were attacked by pirates on the lake on Sept. 30, while they were returning to the U.S. from Mexico on Jet Skis.
Gonzalez, the Zapata County sheriff, has said he has an eyewitness who corroborates her account.
Falcon Lake is a dammed section of the Rio Grande, 25 miles long and 3 miles across. Pirates have robbed boaters and fisherman on the Mexican side, prompting warnings to Americans by Texas state officials, but Hartley's death would mark the first violent fatality on the lake.
That part of Tamaulipas state is overrun by violence from a turf battle between the Gulf Cartel and the Zeta drug gang, made up of former Mexican special forces soldiers, and both are battling the Mexican military.
Dennis Hartley, David Hartley's father, expressed shock and regret at Flores' killing.
"I just, I'm in shock about this right now," he told The Associated Press from his Colorado home. "I really don't have any hope that David will be found. I really hate other people putting their lives at stake. We don't need more sons lost. If this is true, I'm just really heart broken that this happened."
Tamaulipas State Police unit chief Juan Carlos Ballesteros said earlier that Mexican investigators believe brothers Juan Pedro and Jose Manuel Zaldivar Farias might have killed Hartley as he took photos of a sunken church at the lake.
The brothers already were sought for allegedly being in a gang of pirates that operates on Falcon Lake and for terrorizing a Mexican town at the south end of the lake.
Perry said once again that the Hartley incident points to the need for heightened border security by the U.S. federal government.
"The American people have had it up to here with their lack of understanding and their lack of action securing that border, where citizens of both sides can know that they are living in a country where they're going to be safe," he said.