By Terry Frieden,
CNN Justice Producer
Attorney General Eric Holder said Tuesday that the controversial tactic that allowed illegal guns to be smuggled to Mexico "should never have happened, and it must never happen again."
In testimony to the Senate Judiciary Committee, Holder hit hard at the Bureau of Alcohol, Tobacco, Firearms and Explosives practice that has tainted his tenure at the Justice Department, and led to some Republican calls for him to resign.
"I want to be clear: Any instance of so-called 'gun walking' is unacceptable," Holder said of weapons smuggling, later adding: "This operation was flawed in its concept, and flawed in its execution."
Holder acknowledged what critics have been saying about the long-term consequences of "gun walking."