In a probe of arms trafficking during the George W. Bush administration, a federal prosecutor said it was wrong that law enforcement agents had allowed hundreds of guns to go into Mexico and into the hands of drug dealers, according to documents the Justice Department turned over to Congress on Thursday.

The emailed comment by an assistant U.S. attorney in Arizona to a law enforcement colleague in December 2008 focused on the tactic used in Operation Wide Receiver, an investigation that began in early 2006. The newly disclosed internal Justice Department documents show Wide Receiver had many of the same problems that turned up more recently in a separate, later probe called Operation Fast and Furious, which is the focus of an inquiry by congressional Republicans.

The concerns about the earlier Wide Receiver probe that were expressed in the internal Justice Department documents deal with the law enforcement tactic of standing aside rather than arresting "straw" buyers of illicitly purchased weapons in the hopes that agents can follow the guns and straw buyers to major arms traffickers.

The tactic, known as, "letting guns walk," long has been prohibited by Justice Department policy. But federal agents under both the Bush and Obama administrations, nevertheless, turned to the tactic as a response to long-running criticism that traditional department policies have left arms-trafficking kingpins virtually untouched by prosecutors.

In the more recent Fast and Furious investigation, focused on sales at Phoenix-area gun shops, federal agents lost track of nearly 1,400 of the more than 2,000 weapons they were trying to track. Some of those turned up later at crime scenes in Mexico and the United States.

The Wide Receiver investigation that began in early 2006 proceeded and used the gun-walking tactic despite the concerns expressed by some of the law enforcement personnel involved in it.

"I am no longer comfortable allowing additional firearms to `walk,' without a more defined purpose," a supervisor for the Bureau of Alcohol, Tobacco, Firearms and Explosives in Arizona wrote in a June 2007 email to a federal law enforcement official in Texas about Operation Wide Receiver.

"I think it is wrong for us to allow 100s of guns to go into Mexico to drug people knowing that is where they are going," Assistant U.S. Attorney Serra Tsethlikai wrote in a Dec. 19, 2008, email to another assistant U.S. attorney.

Early in the investigation, prosecutors had enough to charge suspects who had been converting firearms into machine guns, but law enforcement officials decided to wait, according to emails by personnel at ATF.

"We believe at this point there is more value in the surveillance, identification of locations, persons, vehicles," an ATF supervisor wrote in a June 15, 2006, email. An ATF briefing paper on Wide Receiver in August 2006 said the weapons involved in the investigation probably had ended up as "illegally trafficked firearms to Mexico."

Investigative activity went on for another year, then languished at the Justice Department until the Obama administration took office.

In an August 2009 email, an ATF agent said that a federal prosecutor had a "moral dilemma" about Wide Receiver because the government had allowed the targets of the investigation "to traffic 300+ firearms to Mexico."

Under President Barack Obama, the Justice Department pursued the Wide Receiver case and six defendants have pleaded guilty, two others who were charged are fugitives and a third fugitive in the case was recently arrested.

There was extensive discussion in the internal documents about the desire to coordinate the Wide Receiver investigation with Mexican authorities _ but little in the documents to indicate that coordination actually took place.

Rep. Darrell Issa of California, the Republican who chairs the House Oversight and Government Reform Committee that is investigating Operation Fast and Furious, has said coordination with the Mexican government on Wide Receiver was "just the opposite" of the manner in which Fast and Furious was conducted, with Mexican authorities in the loop on Wide Receiver but out of the information loop on Fast and Furious.

"It is deeply discouraging that top Justice officials knew such details about problems in Operation Wide Receiver yet were still so quick to dismiss warnings from whistle-blowers" in Operation Fast and Furious, Issa said of the newly released documents.

Another Arizona-based gun-running probe, the Hernandez investigation, was undertaken during the Bush administration after Wide Receiver. Those agents made contact with Mexican authorities and arranged for them to take over surveillance of a vehicle driven by suspected straw purchasers after it crossed into Mexico with weapons purchased in this country, but the Mexican agents claimed they never spotted the vehicle.

Subsequently, ATF officials asked Bush administration attorney general Michael Mukasey to lean on his Mexican counterpart to supply better vetted, incorruptible agents for such operations. Mukasey has declined to say whether he had any success or even whether he tried to do that.

The Hernandez case was run by ATF's Phoenix office, which also later handled Fast and Furious.