It started with one whistleblower, but now involves dozens of investigators, has created a standoff between the Department of Justice and lawmakers and threatens Mexico’s diplomatic relationship with the United States.

Friction is growing over the probe into the failed “Project Gunrunner” program -- run by the Justice Department's Bureau of Alcohol Tobacco and Firearms that intended to stop the flow of guns to criminals in Mexico. Whistleblowers claim the bureau actually encouraged the illegal sale of firearms to known criminals, then allowed those guns to be smuggled to Mexico and tracked.

On Tuesday, Rep. Darrell Issa (R-Calif.) went after Attorney General Eric Holder for refusing to answer questions and subpoenas for documents that implicate who approved the Bureau of Alcohol, Tobacco, Firearms and Explosives project that allowed guns purchased illegally in U.S. to be smuggled into Mexico on behalf of the drug cartels with the knowledge and consent of the ATF.

"We're not looking at straw buyers, Mr. Attorney General, we're looking at you," Issa said. "We're looking at you, we're looking at your key people who knew or should've known about this."

Holder shot back.

"The notion that somehow or another that this Justice Department is responsible for those deaths, that assertion is offensive," Holder said, referring to the death of American Border Patrol Agent Brian Terry.

"What if it's accurate, Mr. Attorney General?" Issa responded. "What am I going to tell Agent Terry's mother about how he died at the hands of a gun that was videotaped as it was being sold to a straw purchaser fully expecting it to end up in the hands of drug cartels?"

Holder responded. "We'll have to see exactly what happened with regard to the guns that are an issue there."

Also on Tuesday, in a letter to the attorney general signed by both Issa and Sen.Charles Grassley (R-Iowa), the Congressmen say they are “disappointed that you do not appear to be taking this issue seriously enough”. Grassley, in a handwritten postscript, tells Holder he is being ‘ill-served’ by staff who are not telling him the whole story.

The theatre on the Hill is an outgrowth of an ongoing investigation that dates back to allegations two months ago from ATF agent John Dodson, a lone voice and career agent who told Fox News in March that the tactic of letting guns "walk" was approved by his supervisors in the Phoenix ATF office over the objections of several agents.

"How many people have to die?" he said. "We don't know where those guns are gonna end up. I've been here since the beginning. Tell me I didn't do the things that I did. Tell me you didn't order me to do the things I did. Tell me it didn't happen."

Dodson was motivated in part by the death of Terry. At the scene of his shooting, police found two AK-47s that were purchased in the U.S. and distributed to drug cartels. These guns were traced to a gun shop that was working with the ATF Project Gunrunner and the Operation Fast and Furious program.

The gun shops say they were encouraged by ATF to sell the guns to suspected straw buyers, an act that is illegal. ATF agents assured the owners the sales were fine and part of an investigation. Unknown to the owners however, the guns were allegedly allowed to flow to Mexico into cartel hands.

The ATF hoped to trace the guns and ultimately make arrests of “bigger fish” in the trafficking network. That apparently never happened. Investigators believe more than 1,800 weapons, including assault rifles, made their way into Mexico, where they were used to commit violent crimes. This disclosure enraged many Mexican lawmakers, who want to sue the gun stores and prosecute U.S. officials who approved the plan.

While Holder and President Obama are content with an internal investigation conducted by the Department of Justice’s Office of Inspector General, others are not.

"When I made complaints against the ATF, they were completely ignored and whitewashed and they left the same people in place to operate Project Gunrunner," says ATF Tucson Agent Jay Dobyns.

Dobyns spent two years undercover with the Hells Angels. While he became a star witness in the prosecution of 15 members of the motorcyle gang on charges ranging from extortion to murder, he also became a target of their revenge.

"You are gonna spend the rest of your life running from the Hells Angels," he says they told him. "We know who you are, we know where you live."

The ATF office in Phoenix, specifically Agent-in-Charge Bill Newell and his deputy, George Gillette, promised to protect Dobyns, but Dobyns says they didn't. He says the Hells Angels threatened to rape his wife and behead his children. Weeks later, Dobyns says the gang burned down his house with his family inside. Miraculously, they escaped.

"They abandoned us, they ignored us," said Dobyns.

He filed a complaint against the ATF. Seeking to contain the damage, the DOJ Office of Inspector General investigated and concluded the agency acted "recklessly, needlessly and inappropriately."

That was in August 2009 against Newell, Gillette and the ATF officials in charge. However, no one was held accountable. Operation Fast and Furious, under the direct authority of the ATF Phoenix Office, was launched less than six months later. Dobyns says allowing the ATF to conduct another OIG investigation would be a mistake

"They do not care what the OIG says. They don't care what the OIG conclusions are."