Documents obtained by CBS News show that the Bureau of Alcohol Tobacco, Firearms and Explosives (ATF) discussed using their covert operation "Fast and Furious" to argue for controversial new rules about gun sales. PICTURES: ATF "Gunwalking" scandal timeline In Fast and Furious, ATF secretly encouraged gun dealers to sell to suspected traffickers for Mexican drug cartels to go after the "big fish." But ATF whistleblowers told CBS News and Congress it was a dangerous practice called "gunwalking," and it put thousands of weapons on the street. Many were used in violent crimes in Mexico. Two were found at the murder...