Updated

Documents released Thursday show that federal agents appeared to have probable cause to arrest the biggest buyer of assault weapons in the Fast and Furious operation -- eight months before Border Patrol Agent Brian Terry's death ended the scandal-ridden program.

Rep. Darrell Issa, R-Calif., and Sen. Charles Grassley, R-Iowa, have demanded Attorney General Eric Holder provide a briefing as to why ringleader Manuel Celis Acosta was not arrested earlier given repeated evidence that he was running guns.

"I think the Department of Justice is the Department of Injustice," Grassley said on Capitol Hill. "They can't expect people to believe that they couldn't arrest this guy."

On April 2, 2010, Phoenix Police stopped Celis Acosta. In the car they found eight weapons, none of which were registered to him. At least one, a Colt .38, had been bought just a few days earlier by Uriel Patino, who had already bought 434 weapons in the previous six months.

It is illegal to buy a gun for anyone other than yourself. The Bureau of Alcohol, Tobacco, Firearms and Explosives has argued it did not have probable cause to arrest Patino or Celis Acosta. These new documents suggest they did, raising new doubts about the agency's desire to actually bust the trafficking ring.

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    Two months later, on May 29, 2010, Celis Acosta was stopped again, this time driving a 2002 BMW 754i trying to cross into Mexico. Inside, border agents found 74 rounds of AK-47 ammunition and nine cell phones hidden in the trunk. ATF Special Agent Hope MacAllister and her counterpart from Immigration and Customs Enforcement, Layne France, released him after he promised to cooperate in the future. MacAllister wrote her phone number on a $10 bill.

    Celis Acosta had been under ATF surveillance since October 2009. He had been a suspect in a Drug Enforcement Administration investigation, but when he began buying guns for the Sinaloa Cartel, the DEA alerted ATF. The two agencies shared a wiretap until ATF got its own. The ATF also set up a camera mounted on a telephone pole outside his home where they watched guns and money change hands in his garage multiple times.

    On April 7, police in El Paso also seized another load of weapons assembled by Celis Acosta. All the guns had been bought in Phoenix by straw buyers under watch by Operation Fast and Furious. Some belonged to Patino, who again appeared to be trafficking weapons.

    ATF managers have told Congress they could not arrest anyone because the U.S. Attorney's Office in Arizona would not allow it since agents lacked probable cause that a crime was committed. They also admit knowingly allowing some guns to be illegally purchased in order to further their investigation.

    Many in Congress don't buy it.

    "If you find somebody carrying a massive number of guns across the border that you didn't have reason to arrest them?" said Grassley. "That just doesn't hold water as far as I am concerned. It doesn't pass the laugh test."

    More than 100 Republicans in the House have signed a resolution asking for Holder to resign.