Senator Chuck Grassley says his staff is “digging…every day” into the federal program that failed to track guns in the U.S. that were sold to Mexican drug runners.

“Trying to follow every lead that we can,” Grassley says, “and these leads have brought us a long ways now, compared to when we started.”

The project was called “Fast and Furious.” Agents in the Bureau of Alcohol, Tobacco and Firearms monitored large gun sales in Arizona, with the goal of tracking the guns to the drug cartels in Mexico. Agents lost track of some of the weapons, one of which was found near the body of a murdered border patrol agent last December. Two officials connected to the program have resigned, but Grassley says Attorney General Eric Holder needs to explain how much he knew about the program, and how early he knew about the problems.

“For instance, the February 4 letter from the Justice Department said that there wasn’t anything to ‘Fast and Furious’ and it was that way even after we showed them documents showing them they were wrong,” Grassley says. “They still wrote us letters in March, saying there wasn’t anything to it.” 

The attorney general has said he knew of the program last year, but it wasn’t until earlier this year that he learned of the problems.

“We just are digging and digging and digging with a goal that we want to make sure that whoever o.k.’ed this gets fired,” Grassley says. “…And, lastly, we want to make sure a stupid program like this doesn’t happen again.”

The Obama Administration has released documents indicating the strategy to track gun sales in the U.S. to drug cartels in Mexico was begun during the Bush Administration. The controversy has become a campaign issue. Republican presidential candidate Rick Perry this week called on Attorney General Holder to resign.

On December 8, the attorney general will testify before the House committee investigating the operation. Grassley will also testify at that House hearing.