[Updated on September 19, 2012] Wednesday's Justice Department inspector general report criticizing 14 ATF and Justice Department employees relates to a months-long investigation into a controversial gun sting that allowed hundreds of weapons to reach violent Mexican drug cartels.

The controversial Operation Fast and Furious, which the Bureau of Alcohol, Tobacco, Firearms and Explosives began in 2009, came to the public's attention after guns linked to the program were found at the site where a U.S. Border Patrol agent was killed.

Brian A. Terry was fatally shot in the Arizona desert, just north of the Mexico border, on December 14, 2010, after he confronted a group of bandits believed to be preying on illegal immigrants. Nearly three months later, Sen. Charles Grassley, R-Iowa, announced that two weapons found near the scene were traced to an ATF gun-running operation, later identified as Fast and Furious.

Fast and Furious was intended to build cases against Mexican drug cartels and the smuggling networks supplying them by allowing illegally purchased firearms to go from the United States into Mexico. In the operation, "straw buyers" - people who buy the weapons for others who might not legally be allowed to buy them - were allowed to purchase in Arizona illegally large numbers of weapons, some of which ended up in the hands of cartels in Mexico.

The idea was that once the weapons in Mexico were traced to the straw purchasers, the smuggling network could be brought down. But the ATF lost track of more than 1,000 firearms, and some guns weren't recovered until they turned up at crime scenes, both in Mexico and, as the Terry case illustrated, the United States.

Once the operation was in the public spotlight, Mexican officials and critics in the United States called the operation a failure, saying it exacerbated the longstanding problem of U.S. weapons getting into the hands of Mexican cartels.

Criticism was heaped on the ATF and its parent agency, the Department of Justice. Congressional committees began investigating last year, and Democrats and Republicans have been at odds over who knew what about the operation, and when.

The House Oversight Committee has sought documents that would show why the Justice Department decided to withdraw as inaccurate a February 2011 letter sent to Congress that said top officials had only recently learned about Fast and Furious.

The Justice Department has turned over thousands of documents during the investigation. However, Attorney General Eric Holder refused to turn over materials containing internal deliberations. In June, the Republican-led House voted to hold the attorney general in contempt.

Here is a timeline of some of the events in the Fast and Furious investigation:

December 14, 2010: Border Patrol Agent Brian A. Terry is killed in the Arizona desert. Two guns found at the site are later linked to the ATF Fast and Furious program.

January 2011: Congress begins asking questions about the ATF program.

February 4, 2011: Responding to an inquiry from Sen. Charles Grassley, Assistant Attorney General Ronald Weich writes that top officials had only recently learned about the ATF gun-running program, but that nothing improper was done in the operation. Weich also asserts that any allegation that the ATF knowingly allowed the sale of assault weapons to a straw purchaser who then transported them into Mexico is false. "ATF makes every effort to interdict weapons that have been purchased illegally and prevent their transportation to Mexico," Weich wrote.

March 3, 2011: An ATF whistleblower tells  "CBS Evening News" that the ATF intentionally allowed guns to go into Mexico. Just minutes before the broadcast, ATF Acting Director Kenneth Melson issues a statement saying the agency is forming a panel to "review the bureau's current firearms trafficking strategies employed by field division managers and special agents."

March 4, 2011: CNN reports that Grassley wrote a letter to Attorney General Eric Holder complaining that the ATF was "stonewalling" his investigation into the matter. CNN also reports that, according to Grassley, ATF agents told his staff "the agency allowed the sale of assault rifles to known and suspected straw purchasers for an illegal trafficking ring near the southwest border."

May 2011: Holder tells the House Judiciary Committee that he "probably heard about Fast and Furious for the first time over the last few weeks."

June 15, 2011: Rep. Darrell Issa alleges Weich's claim that the ATF never knowingly allowed the sale of assault weapons to straw purchasers, who then transported them into Mexico, is deceiving. Issa, chairman of the House Oversight and Government Reform Committee, and other congressmen allege that although it is technically true that straw purchasers didn't cross any weapons into Mexico, they did transfer them to third parties who did.

Also, ATF whistle-blowers testify before Issa's committee. Peter Forcelli, a supervisor at the ATF Phoenix field office, says Fast and Furious was "a colossal failure of leadership." An agent, Lee Casa, tells the committee that ATF supervisors brushed off several agents' concerns over letting guns go. Another agent, John Dodson, tells lawmakers: "I cannot begin to think of how the risk of letting guns fall into the hands of known criminals could possibly advance any legitimate law enforcement interest."

August 30, 2011: Melson, the ATF's acting director, is reassigned to a position in the Justice Department. Also, the U.S. attorney for Arizona, Dennis Burke, resigns. Burke's office had given legal guidance to the ATF relating to Fast and Furious.

September 7, 2011: Holder says in a news conference that Fast and Furious "was clearly a flawed enforcement effort," and adds that investigations will find involvement did not reach "the upper levels" of the Justice Department.

October 12, 2011: Congressional investigators issue a subpoena for communications from several top Justice Department officials, including Holder, relating to Fast and Furious. Meanwhile, Republicans say that previously released documents show that Holder knew about Fast and Furious much earlier than he indicated to the House Judiciary Committee in May. Holder and his aides deny the allegation.

November 1, 2011: Lanny Breuer, an assistant attorney general in charge of the criminal division, tells a Senate judiciary subcommittee that he first learned of the tactic of allowing illegally purchased guns to leave shops in April 2010. That tactic, he said, was executed during a 2006-2007 ATF program, called Operation Wide Receiver, which happened during the George W. Bush administration.

Breuer says he should have warned Holder and other Justice officials about the 2006-2007 tactics, but failed to do so. He said he also failed to recognize that the same tactics used in 2006-2007 were being used again in Fast and Furious.

November 8, 2011: Holder tells the Senate Judiciary Committee that the tactic allowing illegal guns to be smuggled into Mexico "should never have happened, and it must never happen again."

December 2, 2011: The Justice Department withdraws its February 4 letter to Grassley, saying the letter contains inaccuracies.

Also, ahead of a December 8 House Judiciary Committee hearing at which Holder is to testify, 1,400 pages demanded by investigators are released. The documents show, among other things, that Justice officials struggled for days over how to write the February letter to Grassley.

December 7, 2011: Grassley calls on Breuer to resign, saying he misled Congress by saying he didn't know in February that the assertions in the February 4 letter were wrong. Grassley says documents show that Breuer should have been aware that the letter contained false assertions, due to his knowledge of the 2006-2007 Operation Wide Receiver.

December 8, 2011: Holder tells the House Judiciary Committee that he won't resign over the Fast and Furious controversy, and that he doesn't think any of his top aides should step down. He says the operation relied on "unacceptable tactics" and was "inexcusable," but he says that Justice Department officials have cooperated with investigators, and that any previous misleading information was not part of an intentional deception.

January 31, 2012: Democrats on the House Government Oversight and Reform Committee issue a report saying the panel has found no evidence showing that top Justice officials "conceived or directed" Fast and Furious. The report from the Democrats, who are a minority on the Republican-led panel, places blame for the program on federal agents and prosecutors in Arizona.

February 1, 2012: Terry's parents, Josephine and Kent Terry Sr., file a $25 million wrongful death claim in an Arizona court against the federal government.

February 2, 2012: Holder tells the House Oversight and Government Reform Committee that firings of Justice officials who oversaw Fast and Furious are likely to come in the next six months.

Meanwhile, Issa threatens to begin a contempt proceeding against Holder unless he releases more documents.

May 18, 2012: Issa and other House GOP lawmakers send Holder demanding that he release the full amount of materials that Issa's committee asked for previously.  Although the letter acknowledges that there's been some cooperation on the investigation, it emphasizes that House Republicans still want answers in two key areas - who in top positions knew about the operation before the murder of a federal border agent exposed its existence, and did anyone on Holder's team misinform Congress when they responded in part to the Oversight committee's subpoena.

June 19, 2012: A showdown meeting between Holder and Issa fails to resolve their dispute over documents. Issa says that unless at least some of the documents are handed over before the committee meets June 20, it would vote on a measure that would send a contempt vote to the full House.

June 20, 2012: President Barack Obama asserts executive privilege over some of the documents sought by Issa's panel. The White House move means the Department of Justice can withhold some of the documents.

The House Oversight and Government Reform Committee votes 23-17 (with all of the panel's Republicans voting yes, and all of the panel's Democrats voting no) to recommend that the full House vote on whether to cite Holder for contempt of Congress. The vote by the full House could happen on the week of June 25.

June 28, 2012: The House votes to hold Holder in contempt of Congress, but he does not face criminal prosecution. House Republicans are joined by 17 Democrats in citing Holder, while dozens of Democrats walk out in protest.

The House also cites Holder for civil contempt to give it the option of filing a lawsuit compelling Holder to turn over documents sought by Oversight Committee investigators.  Issa concedes that investigators lack any evidence that Holder knew of the failed weapons-tracking tactics of Fast and Furious.

July 9, 2012: Federal authorities unseal an indictment charging five men in Terry's death.

The indictment charges Manuel Osorio-Arellanes, Jesus Rosario Favela-Astorga, Ivan Soto-Barraza, Heraclio Osorio-Arellanes and Lionel Portillo-Meza with first-degree murder, second-degree murder, conspiracy to interfere with commerce by robbery, attempted interference with commerce by robbery, carrying and using a firearm during a crime of violence, assault on a federal officer and possession of a firearm by a prohibited person. A sixth defendant, Rito Osorio-Arellanes, is charged solely with conspiracy to interfere with commerce by robbery.

Up to $1 million is offered for information leading to the arrest of four men still at large.

September 19, 2012: The U.S. Justice Department's inspector general issues a report finding 14 ATF and DoJ employees responsible for management failures in the Fast and Furious operation. The report refers the 14 for possible disciplinary action, but did not recommend criminal sanctions.

The report also finds that Holder was not informed of the operation until 2011, after Terry's December 2010 death.

Also, Holder announces that Melson, the acting ATF director, has retired, and that former Deputy Assistant Attorney General Jason Weinstein has resigned.