"The Justice Department has yet to respond to any of Congress' questions about what happened in Reno for more than a year," Grassley said. "It's an abdication of responsibility on the part of the Justice Department, and if these crimes weren't prosecuted, whether because of actions of the U.S. Attorney or the ATF, the people of Nevada should know why."

The letter is the latest reaction to press reports that a rift between the U.S. Attorney's office in Reno, Nevada and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) has prevented these gun-trafficking cases from being prosecuted.

Several reports have said federal prosecutors have refused to prosecute gun-related cases brought forward by ATF agents. Some of these reports have said this problem has been caused by a turf battle between the two agencies, which has led some ATF agents to seek transfers out of Nevada.

The GOP letter cited reports that U.S. Attorney Daniel Bogden and ATF Acting Director B. Todd Jones released a statement on Sept. 28 that tried to address reports about the inter-agency fight. That statement said the U.S. Attorney's office was accepting all cases referred to it by the ATF.

It also said the two agencies were reviewing allegations of non-cooperation, and would "work to address any issues that could impact the effectiveness of their law enforcement efforts to protect the public from violent crime."

But the letter said Congress was not made aware of this statement, and said Congress still has no understanding about what that statement means for the dozen or so outstanding cases.

As a result, the letter asked Holder to say whether the U.S. Attorney's office would reconsider any of the ATF cases, how long this might take, and who will review them.

"In the course of the U.S. Attorney's Office's dispute with ATF, how many of the ATF cases declined by the U.S. Attorney's Office would be barred within the next six months by statutes of limitations?" it asked. "For each such case, precisely when would the statute of limitations expire?"

Grassley, Heller and Amodei asked Holder to respond to these questions by Oct. 25.