Because the murder happened on the Mexican side of a lake that straddles the U.S.-Mexico border, Zapata County Sheriff Sigifredo Gonzalez Junior says it has been difficult to obtain information from authorities south of the border.
"I don't really think Mexico ever really started an investigation," Gonzalez said.
The Austin-based private intelligence agency STRATFOR put out a report indicating Hartley's body and personal watercraft may have been destroyed shortly after he was killed.
"It is my belief that David's body will never be found," Gonzalez said. "The body does not exist. The body disappeared. There's no body."
The Mexican government suspended the case shortly after Hartley's murder, when a lead investigator was decapitated.
Sheriff Gonzalez has managed to uncover details about the case. He obtained a photo taken from an aircraft he says was "in the area," minutes after the shooting. The photo shows several men matching Hartley's description of the attackers.
"We have identified, in total, about five individuals," Gonzalez said.
Sheriff Gonzalez believes the suspects are members of the Zetas, a violent drug trafficking organization that controls Falcon Lake. Gonzalez has said they may have mistaken David and Tiffany Hartley for rival cartel members.
Gonzalez recently announced he will not seek re-election for Sheriff due to financial reasons.
Tiffany Hartley and Pam Hartley returned to the 60-mile reservoir Tuesday, which straddles the United States and Mexico, to mark the one year anniversary of David Hartley's death.
"A year later we still feel like it's a nightmare," Tiffany Hartley said.
David Hartley's brutal murder at the hands of suspected Mexican cartel members on September 30, 2010 put the spotlight on a border region plagued by drug violence.
"It's hard to believe it's been a year," Pam Hartley said in tears. "I miss him so much."
David and Tiffany Hartley took their personal watercraft to Falcon Lake, on what she has described as a "quiet day" on the water. It was supposed to be one final day of fun on the water.
The couple, who had been married for eight years, had plans to move back to Colorado after living along the border for two years.
David worked for a U.S. oil and gas company which had facilities in Reynosa, Mexico. Drug violence prompted the couple to relocate just across the border to McAllen, Texas.
David and Tiffany had visited Falcon Lake before. Tiffany says David wanted to go back to photograph a partially submerged church on the Mexican side of the lake.
"I just remember his big grin. And he just looked so happy," Hartley said. "Such a beautiful lake and it reminds me of the worst day of my entire life."
As they left the church in an area of Mexico known as Old Guerrero, Tiffany says they were approached by a group of armed men in boats, later identified as suspected Zeta cartel members.
Hartley says the men opened fire, shooting David in the head.
"The moment I saw him being thrown off the jet-ski," Tiffany Hartley said. "Right then and there I knew he was gone. That image will always be there. I think it will always be there forever."
Tiffany says David's body was too heavy for her to lift out of the water.
"I didn't know what to do," she said. "And I have replayed that day in my mind."
Soon after, Tiffany says the men began chasing her and she had no choice but to leave David behind.
Warning signs are now posted near the Falcon Lake boat ramp. But there are fewer fishermen in the water.
"It brought a lot of negative publicity to Zapata," Gonzalez said. "It is still hurting tourism, certainly."
Gonzalez insists the U.S. side of the lake is safe, and he is trying to encourage anglers to return to the U.S. side of the lake.
"Falcon Lake is relatively safe on the US side of the border," Gonzalez said. "We have one of the best bass fishing in the nation."
Violence on the Mexican side of Falcon Lake flared up again this year.
In May, Mexican Marines patrolling the lake discovered a drug gang camp on an island, provoking a gun battle that left 13 people dead, the Mexican Navy said.
One Marine and 12 suspected gunmen of the Zetas drug cartel were killed in the battle.
The Navy said the gunmen opened fire first when the marines discovered the camp, which the gang is believed to have used as a launching point for smuggling marijuana into Texas by speedboat. Marines seized more than 20 guns after the shootout, including several assault rifles.
In August, two Americans ended up with a bullet hole in their boat after a confrontation with a group of men dressed in Mexican Military uniforms.
"A U.S. fisherman went into Mexico with his grandson and he got shot at," Gonzalez said.
The Americans were not injured and were allowed to return to the United States.
Zapata County Sheriff Sigifredo Gonzalez Jr. says the incidents were in the same general area where David Hartley died.
Tiffany Hartley now lives with her parents at their farm in La Salle, in Weld County.
She has received support from numerous lawmakers, and was invited to testify Monday at a congressional field hearing on border security in Brownsville, Texas, which was organized by Representative Ted Poe, R-Texas.
"I wanted them to know who David was," Hartley said.
Hartley says she has requested information about her case from the federal government, but has been stonewalled.
"It's disgraceful. It's absolutely disgraceful," said Sean Dunagan, a Senior Investigator with Judicial Watch.
The organization, which investigates corruption, helped Tiffany Hartley file a lawsuit against the State Department, Justice Department, and the FBI. The lawsuit seeks the results of a Freedom of Information Act Request filed this summer.
"We're trying to force them to give Mrs. Hartley the information about what they're doing to investigate her husband's murder," Dunagan said.
Tiffany and Pam Hartley took a bouquet of white roses to Falcon Lake and threw them in the water to honor David's memory.
"Honey I miss you so much," Tiffany Hartley said in tears. "You will forever be in my heart."
(KUSA-TV © 2011 Multimedia Holdings Corporation)