Washington (CNN) -- Congressional Republicans sought Wednesday to expand their investigation of the controversial ATF-approved illegal sale of firearms in Arizona to include an apparently similar operation in Texas.
In both cases, illegally-sold weapons were allegedly allowed by the Bureau of Alcohol, Tobacco, Firearms and Explosives to "walk" across the U.S.-Mexico border, and ended up likely being involved in the killing of U.S. agents.
In the Texas case, Immigration and Customs Enforcement Agent Jaime Zapata, who was working for the United States in Mexico, was murdered February 15 when his vehicle was ambushed by about 10 gunmen on a major highway between Mexico City and Monterrey.
Tuesday, Sen. John Cornyn, R-Texas, said he wanted to know if a Texas-based "gun walking" program may have played a role in Zapata's murder.
"One of the weapons used to murder the agent was (allegedly) purchased by Texas resident Otilio Osorio, and trafficked through Laredo to Mexico," Cornyn said.
He said he has been unable to get an answer from the Justice Department, so Tuesday he asked the leaders of the GOP investigation, Rep. Darrell Issa, R-California, and Sen. Charles Grassley, R-Iowa, to take action.
Wednesday, Issa and Grassley sent a letter to Attorney General Eric Holder demanding answers to a series of questions and requiring the Justice Department to produce documents on the Texas gun operation by November 8.
Issa and Grassley have been investigating the Arizona-based ATF operation known as Fast and Furious in which two weapons sold illegally were allowed to be transported into Mexico and ended up at the murder scene of Border Patrol Agent Brian Terry last December.
Holder has said it is a violation of Justice Department policy for illegal weapons to be allowed to travel out of gun shops, even if the purpose is to track them to drug cartels.
The Justice Department on Wednesday acknowledged receipt of the new letter from Issa and Grassley and said it is "being reviewed."
Department of Homeland Security Secretary Janet Napolitano largely deflected a series of pointed questions Wednesday when asked about the Arizona-based Operation Fast and Furious by Issa during House testimony.
Napolitano said her top concern in the wake of the Terry shooting was finding the killers, and she met promptly with the FBI and federal prosecutors. She said she would await the Justice Department inspector general's report on details of the gun operation. That report is expected by the end of this year.