ATF "Gunwalking" scandal timeline

Mexico drug war — AP Photo/Felix Marquez

Sept. 2009: In an effort to stem the rising tide of violence caused by Mexican drug cartels, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) Phoenix office begins its controversial Operation "Fast and Furious." The idea is to encourage gun dealers to sell to suspected traffickers for Mexican drug cartels and see where the guns end up. The goal is to try to take down a major cartel. But the so-called "gunwalking" becomes increasingly controversial among ATF agents ordered to take part.

This undated photo provided by U.S. Customs and Border Protection shows U.S. Border Patrol agent Brian A. Terry. — AP/U.S. Customs and Border Protection

Dec. 14, 2010: Border Patrol Agent Brian Terry is gunned down in Arizona near the Mexico border. At least two assault rifles from an ATF operation Fast and Furious are on the scene, but the public isn't informed of the connection.

Senator Chuck Grassley, R-IA, questions a witness during a Senate Judiciary Committee's Antitrust, Competition Policy and Consumer Rights Subcommittee, hearing on the AT&T/T-Mobile merger, on May 11, 2011 in the Dirksen Senate Office Building on Capitol H — Mark Wilson/Getty Images

January, 2011: After being approached by a number of ATF whistleblowers, Sen. Charles Grassley, R-Iowa, begins an investigation into Fast and Furious gunwalking allegations.

ATF agent who was killed, Brian Terry — CBS

Feb. 23, 2011: CBS News airs its first report on the alleged gunwalking during Fast and Furious, quoting at least 11 ATF agents and senior managers who did not wish to be named. They say they repeatedly warned superiors that the gunwalking plan was dangerous and a federal agent could end up getting shot with one of the walked weapons. One agent told CBS News, "The numbers are over 2,500 on that case

ATF Agent goes on record about guns — CBS

March 3, 2011: ATF Special Agent John Dodson blows the whistle on the "gunwalking" operation and its link to Terry's death, in an exclusive interview with CBS News. Dodson defies officials who say it never happened telling CBS News, "I'm here, boots on the ground in Phoenix telling you we

Firearms sold in Operation Wide Receiver — Mike Detty

March 8, 2011: CBS News reports on a second alleged ATF gunwalking operation called "Wide Receiver" in Tucson. It's also run out of the Phoenix office and dates back to at least 2008 under the Bush Administration. WATCH: Sharyl Attkisson's report

Responding to operation "Fast and Furious," President Obama told Univision's Jorge Ramos, "serious mistakes" may have been made, March 23, 2011. — Univision

March 27, 2011: President Obama tells Univision, a Spanish language network, that neither he nor Attorney General Eric Holder knew of or approved Fast and Furious. "There may be a situation here which a serious mistake was made," said President Obama, "and if that's the case then we'll find out and we'll hold somebody accountable."

May 3, 2011: At a House Judiciary Committee hearing on an unrelated topic, Rep. Darrell Issa, R-Calif., asks Attorney General Holder when he first heard of Fast and Furious. Holder answers: "I'm not sure of the exact date, but I probably heard about Fast and Furious for the first time over the last few weeks." That answer is later called into question based on memos directed to Holder nearly a year earlier. WATCH: Holder's response

Josephine Terry, mother of murdered Border Patrol Agent Brian Terry, appears at a Congressional hearing led by Rep. Darrell Issa, R-Calif.

June 15, 2011: Terry's family appears at a Congressional hearing led by Rep. Darrell Issa, R-Calif.. They say they've been given no answers in the murder. A Justice Department representative Ronald Weich tells Congress that his agency has complied with and cooperated with the House Oversight Committee's investigation thus far.

CBS/AP

Aug. 29-30, 2011: ATF Director Kenneth Melson is reassigned and the U.S. Attorney for Arizona who oversaw Fast and Furious, Dennis Burke resigns. Read Sharyl Attkisson's blog

Nov. 1, 2010 memo from Lanny A. Breuer to the Attorney General, Eric Holder. — CBS News

Oct. 3, 2011: CBS News reports on Justice Department memos to Holder mentioning Fast and Furious as early as July 2010. Read Sharyl Attkisson's blog The memos seem to contradict Holder's May testimony that he had just recently learned of Fast and Furious. Other documents show senior Justice officials were familiar with Fast and Furious.

Oct. 5, 2011: CBS News reports further on Operation "Wide Receiver," in an exclusive interview with a confidential informant for ATF who said the agency was letting guns walk as early as 2006. WATCH: Sharyl Attkisson's report

Oct. 7, 2011: Holder sends a letter to Congress explaining that he never saw the memos mentioning Fast and Furious, and that top Justice Department officials who were briefed on the case didn't know about the controversial "gunwalking" tactics being used.

Nov. 8, 2011: Attorney General Holder testifies at Senate Judiciary hearing and admits to Congress for the first time that gunwalking happened in Fast and Furious. He also tells Senators that his agency's initial letter to Congress denying gunwalking last February was "inaccurate." WATCH: Eric Holder's testimony