By APRIL CASTRO, Associated Press Writer April Castro, Associated Press Writer – 1 hr 31 mins ago

ZAPATA, Texas – The Mexican government said Friday it has opened a federal investigation into the reported shooting of an American tourist on a border lake plagued by Mexican pirates and strongly denied accusations it has delayed action on finding the man or his attackers.

A statement from Mexico's Ministry of Foreign Affairs "categorically rejects claims to the effect that Mexican authorities are not doing enough to find" David Hartley.

Hartley's wife, Tiffany, says she and her husband were riding Jet Skis back from Mexico on Sept. 30 when they were attacked by Mexican pirates in speedboats who opened fire and shot David Hartley in the back of the head. He fell into the water. Tiffany Hartley has said she tried to rescue him but fled to the U.S. side of the lake as the pirates continued shooting.

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 by Texas state officials, but Hartley's death would mark the first violent fatality on the lake.

The foreign ministry's statement said the federal attorney general's office has opened an investigation based on Tiffany Hartley's testimony to Mexican consulate officials in McAllen, Texas, where she lives.

In the Hartleys' previous home state of Colorado on Friday, about 100 friends, relatives and supporters gathered at a Denver park ahead of a planned march to that city's Mexican consulate, where they hoped to encourage the Mexican efforts to find Hartley's body.

The Mexican army, federal police and state and local authorities — using speedboats, helicopters and all-terrain vehicles — have been searching since last week, authorities said.

Ruben Rios, a spokesman for the state prosecutor's office in Tamaulipas, said the search continues during daylight hours, but is suspended at night because of winds and waves. U.S. authorities said the search also has been hampered by threats from drug gangs.

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.

"The search will continue for several days," Rios said. "The search for this person will be intensified."

U.S. Rep. Henry Cuellar on Thursday told reporters Mexican authorities were doing everything they could while trying to keep their own crews safe.

"When darkness was falling (Wednesday evening), they got word that there might be an ambush," Cuellar said. "People that are trying to do their job on the Mexican side are facing a risk, they're right inside the hornets' nest ... they had to suspend the search."

Texas Gov. Rick Perry began Friday to soften his "no excuses" stance, saying through a spokeswoman that he was "grateful" for news Mexico had stepped up its search efforts, calling them "significant and very helpful."

But, said spokeswoman Katherine Cesinger, "I don't think anyone will be satisfied until a body is recovered."

Earlier this week, Perry had said he expected Mexican President Felipe Calderon to call him within 48 hours to report a body had been found and that even the threat of drug gang violence against search crews was no reason to halt the efforts.

Jesus de la Garza, Tamaulipas state deputy attorney general, said late Thursday that Mexican authorities had increased their efforts under orders from Tamaulipas Gov. Eugenio Hernandez, whose office was contacted by a member of Perry's staff.

Zapata County Sheriff Sigifredo Gonzalez said he has sent word to the Zetas that he wants Hartley's body returned.

"We cannot arrest anybody for what happened in Mexico, we cannot prosecute on the state level anybody for what happened in Mexico. We just want a body," Gonzalez said. "I did send word to the drug cartel, the Zeta cartel in Mexico, I sent word to them unofficially. I can't tell you how but I sent word to them."

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