(CBS) There's still no sign of David Hartley, the man believed to be dead after a lake pirate attack two weeks ago while he and his wife were jet skiing on the U.S.-Mexico border. But now, the search itself has turned deadly.

CBS News correspondent Don Teague reported from McAllen, Texas that Rolando Flores, lead investigator with the Mexican State Police of Tamaulipas was murdered.

Sigifredo Gonzalez, sheriff of Zapata County, Texas, told reporters on Tuesday Flores' head was "delivered to the army garrison in a suitcase."

Flores reportedly fed information about the case to the media. And it's believed that's why he was slain, Teague reports.

Tiffany Hartley, David Hartley's wife, said on "The Early Show" Wednesday she is heartbroken that people would kill Flores.

She said, "It's hard because, you know, just last week, I met him and I was sitting right next to him and we were communicating through a translator and you could tell he wanted to help and he was sincere and he was compassionate. And, I mean, he was doing his job ... and my heart goes out to his family, because they're having to go through what we're going through right now."

Teague reported Mexican authorities have denied Flores' murder was directly related to the Hartley case. They say he was also working several other important investigations.

U.S. officials, Teague reported, suspect the Zeta drug cartel is behind both murders. The Zeta cartel is a gang formed by a group of Mexican special forces deserters that is violent and extremely territorial.

Fred Burton, vice president of Counterterrorism and Corporate Security for STRATFOR, an intelligence company, said, "What they were trying to do is let everybody know, from the U.S. government to the Mexican authorities, that this is their geography, this is their gateway into the very lucrative North America market. Stay out."

On "The Early Show" Congressman Ted Poe, (R-Texas), who has been involved extensively in this case as well as ongoing border issues, agreed.

"They are not only trying to send a message to Mexico, they're trying to send a message to the United States to back off, that this is their turf, and they want to make sure that they control it and anybody that tries to interfere will pay the price. And, of course, we cannot be intimidated by the Zeta cartels or anyone else. And, if anything, the United States ought to give more resources to this investigation. Mexico needs to let the United States, also, help them in this investigation. So, we cannot be intimidated but that is their message to the United States and to Mexico."

So will this beheading affect the Mexican authorities' willingness to continue a full-force search for Hartley?

Poe said, "Well, that's the problem that Mexico faces now, whether they're going to back off. And this is not the first time the Zetas have done this type of beheading of law enforcement officers to show that they control the border. The Mexican government and, really, the United States, don't control it, either. But, yes, this is a violent operation, but we cannot just say, 'OK, it's violent, we can't do anything about it.' We need to use all of our resources possible to make sure that we shut down the Zeta cartel and make sure they don't murder any individuals whether they're Americans or whether they are Mexican nationals."

Poe, who asked for American help to search the Mexican side of Falcon Lake, said he hopes the U.S. will make resources available in the search for Hartley's body.

He said, "The State Department, I think, was slow coming to the table on this issue, but this is an international issue. It is a terrorist event that is occurring both in Mexico and the United States, and we should deal with these people as terrorists."

Texas governor Rick Perry also told reporters he hopes Mexican authorities increase their efforts to find Hartley's remains.

That's all Hartley's family wants.

Tiffany told reporters, "We're standing in our faith and standing in belief that we are going to see a miracle here, but we also have to realize maybe that's not going to happen."

On "The Early Show," Pam Hartley, David's mother, said she's hoping a full-force investigation continues.

"I hope the Mexican government pursues finding who did this to (Flores) and make it right. He was trying to make his country better, and it's like they need to find who did this to him, as well," she said.

"Early Show" co-anchor Maggie Rodriguez asked Tiffany, "Are you scared for your own safety?"

She said she doesn't feel frightened right now, but said she would if she were to go to Mexico.

"That decision has kind of been made as a family that that will not happen. I will not go to Mexico," she said. "It's just not safe for me to do that."

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