Attorney General Eric Holder went on the defense today over the Justice Department's handling of "Operation Fast and Furious," the investigation that followed gun purchasers across the border into Mexico.

The weapons later ended up at crime scenes in Mexico and the United States, including the murder of a border patrol agent.

Holder testified today before the Senate Judiciary Committee. He admitted the operation was flawed and should have never happened, adding it "must never happen again."

He also expressed regret for sending Congress a misleading letter rejecting the problems with the operation.