Last month's murder of an American citizen on the sprawling Falcon Lake highlighted what some say is a weak spot in our national security.

Only six hours fromHouston,Falcon Lake is simultaneously one of the most popular tourist spots in the state and one of the most heavily used smuggling routes by the Mexican drug cartels.For years, local law enforcement has been begging for extra help, but it took this recent murder to spur a surge in border patrol agents patrolling the area.

"You hear this, you hear that. You don't know what's true. You don't know what to believe," said Pam Hartley when asked about the murder of her son, David.

David Hartley and his wife Tiffany'sattraction to Falcon Lake is easy to see.This is aportion of the Texas-Mexico border where the sun casts an amber glow over willows and soft waves. A 60-mile stretch of the Rio Grande forms a basinrich with fish and the offer of a relaxing day on the water.

"It's not safe for anybody because the drug cartels own this portion of the lake," Houston U.S. Rep. Ted Poe said, referencing the spot on the lake where the Hartleys were attacked.

Armed with automatic rifles,Texas Game Wardens, Zapata County sheriff's deputies and border patrol agents crisscross each other on a lake that is now empty; tourists driven away by fears of Mexico's drug war spilling into the US.

The Hartleys rode their jet skisinto Mexican waters to snap pictures of a partially submerged church in Old Town Guerrero, a spot long admired by shutter bugs on both sides of the border. Zapata County sheriff's investigators said Tiffany Hartley told them they were attacked by armed men in boats as they were leaving the area. Tiffany Hartley told detectives her husband was shot and, as she tried to pull his body from the water, the men kept firing. Fearing for her life, Tiffany Hartley said she sped back across the border, pursued by the gunmen.

"I just kept hearing God tell me, 'You have to go, you have to go,'" Hartley said during an interview earlier this month.

Both state and county law enforcement officers told Local 2 Investigates that one boat continued pursuing Tiffany Hartley into U.S. waters and gave up the chase when she made it shore. U.S. authorities have since warned boaters not to cross into Mexican waters.

"It shows you how bold they are; it shows how they feel they control certain portions of the lake," said Poe during a recent visit to the lake to meet local and state law enforcement officers.

"Do we have enough resources to protect American lives on this part of the Texas-Mexico border?" investigative reporter Robert Arnold asked.

"We need more resources," Poe answered.

This is not the first timeLocal 2visited Falcon Lake. For years,Zapata CountySheriff Sigifredo Gonzalez has been asking the federal government for more help. In the past year there have also been other reports of so-called pirate attacks on the lake.It wasn't until David Hartley's murder that the number of border patrol agents working that area more than tripled.

AsLocal 2rode aboard aTexas Parks and Wildlife plane,it was easy to seethe sprawling and unforgiving terrain sheriff's deputies, border patrol agents and game wardens have to contend with. Smugglers try to blend in with fishing boats.

"It's so hard to patrol up and down here, especially at night," said a pilot with the Parks and Wildlife Department.

With automatic riflesalways at the ready,sheriff's deputies took Local 2 Investigates through thick brush to show several desolate spots where smugglers use the lake and narrow parts of the river to move drugs across.

"Some of us in Washington take this matter seriously, others still live in Never Neverland and claim that the border is safe and secure," said Poe.

Tiffany Hartley has now moved back to her home state of Colorado. She said she is left with the uneasy hope that Mexican authorities will bring her justice.

However, it is unlikely David Hartley's body will ever be found.

"We just keep hoping and praying they're doing what they say they're doing," said Tiffany Hartley.

While no one knows to a 100 percent certainty why the Hartleys were attacked, U.S. officials believe the couple was spotted by low-level members of the Zeta cartel who thought they were spies for a rival cartel when they saw them taking pictures. The search for David Hartley's body was called off shortly after the lead investigator in the case on the Mexican side was found decapitated. Federal and local law enforcement officials believe that was a warning from theZetas to let the matter drop and a message that the men responsible for the shooting would be dealt with by the cartel.

"I don't know if we can believe that or not because the information that we get comes from the drug cartels," said Poe.

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