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Advocates for stronger border security on Wednesday called for stepping up the U.S. offensive to stop murderous drug cartels terrorizing Mexico after an Immigrations and Customs Enforcement agent was killed a day earlier.

"This tragic event is a game changer. The United States will not tolerate acts of violence against its citizens or law enforcement and I believe we must respond forcefully. This should be a long overdue wake-up call for the Obama administration that there is a war on our nation's doorstep," said Rep. Michael McCaul, R-Texas.

McCaul's comments came after Homeland Security Secretary Janet Napolitano and Attorney General Holder announced they are establishing a joint task force to be led by the Federal Bureau of Investigation to help Mexico track down and capture the perpetrators in the murder of ICE Special Agent Jaime Zapata and wounding of another agent.

"This joint task force reflects our commitment to bring the investigatory and prosecutorial power of the U.S. government to bear as we work with the Mexican government to bring these criminals to justice," Napolitano said.

Earlier in the day, President Obama offered his condolences to the parents of Zapata, who was murdered Tuesday when gunmen fired on the vehicle he was riding in with the second agent, who was shot in the arm and leg and is in the hospital in the United States.

"The president called the parents of Special Agent Jaime Zapata to send his and Michelle's heartfelt condolences on the loss of their son yesterday," White House spokesman Nick Shapiro said Wednesday. "The president said that Special Agent Zapata's service and sacrifice will be remembered, and that the U.S. will work with the Mexican government to bring the assailants to justice."

Zapata, who joined ICE in 2006, was on assignment in Mexico City from his post in Laredo, Texas, where he had been a member of the Human Smuggling and Trafficking Unit as well as the Border Enforcement Security Task Force. The two agents were traveling between Mexico City and Monterrey in a car that displayed diplomatic plates.

Members of the Department of Homeland Security, which houses ICE, also offered their condolences to the family of Zapata, who was previously a U.S. Border Patrol agent in Yuma, Ariz.

"We are saddened and outraged at the senseless and cowardly attack today on two ICE agents performing duties in Mexico. We stand together with our brothers and sisters at ICE in condemning these despicable acts and remain all the more committed to our unified efforts to dismantle these criminal organizations," said Customs and Border Protection Commissioner Alan Bersin.

"May the work we continue to do as an agency be worthy of a sacrifice as great as the one made by Special Agent Zapata," said ICE Director John Morton.

U.S. officials say the gunmen knew they were attacking law enforcement officers. A law enforcement official speaking on condition of anonymity told The Associated Press the impression comes from comments attackers made before they opened fire on the agents.

Because the attack occurred on Mexican soil, Mexican authorities have jurisdiction in the investigation. However, Napolitano said the full resources of her department "are at the disposal of our Mexican partners in this investigation."

But that assistance may not be enough. While a U.S. law enforcement authority hasn't been killed on Mexico soil since 1985, what was previously considered unthinkable by would-be attackers -- over fear of full retribution by the United States -- no longer seems to intimidate in a drug war that has killed more than 34,000 people, including dozens of Americans.

"We've got to find the individuals who committed these atrocious acts, we've got to prosecute them to the fullest extent of the law, and then we've got to shut these cartels down" and persuade Mexico to do more, said Julie Myers Wood, a former head of ICE and president of Immigration and Customs Solutions.

Noting that the Mexican authorities are doing all they can with what they had, Wood said Mexico needs a law enforcement surge. At the same time, she added that the U.S. has to be unified in its effort to take down the cartels, and use more intelligence, while at the same time not giving away a strategic advantage.

"What intelligence are we sharing? How does the Zeta cartel know that these ICE agents were driving down this road? Who knew that and why were they targeted? We have to be quieter about that information," she said, adding that it's necessary to assess whether the Mexicans have sufficient intelligence analysts and equipment to target the cartels effectively.

In the 1985 case, U.S. officials went into Mexico and brought out those responsible for the murder of Drug Enforcement Administration officer Enrique "Kiki" Camarena. The assailants were tried in the United States, sending a signal that the U.S. would not go easy on Mexican drug criminals.

"That was significant then," said Jayson Ahern, a former Customs and Border Patrol agent. "The killing of a U.S. law enforcement agent is going to be something that is going to be a significant change. We'll have to see as far as what is going to be the response of the U.S. government going
forward."

Ahern, who said the Mexican government is doing all it can with the help of the combined resources of the Justice, Homeland Security, State and other U.S. departments -- and their offices around the world, added that Zapata's work must continue so that "our borders are not the first opportunity to engage in criminal activity. There is a lot of lateral support."

To that end, Rep. Henry Cuellar, D-Texas, whose district borders Mexico, said that the U.S. must work with the Mexican government to prosecute the crimes and support institutions that combat criminal elements. Cuellar said that new provisions under discussion for DHS are targeted at "an improved path" on effective border policies and practices and making sure the "'bad guys' don't even make it to our borders."