Federal agents based in Phoenix, not officials at Justice Department headquarters in Washington, were responsible for the controversial tactics used in the gun operation known as “Fast and Furious,” Democrats on the House Oversight and Government Reform Committee said in a report released Tuesday.

A year after it became known that the operation relied on a tactic known as gun walking, the 89-page report called Fast and Furious “reckless and fatally flawed.” It puts the blame squarely on the Phoenix office of the Bureau of Alcohol, Tobacco, Firearms and Explosives. It also concludes that the strategy began as early as 2006.

“Contrary to repeated claims by some, the Committee has obtained no evidence that Operation Fast and Furious was a politically-motivated operation conceived and directed by high-level Obama Administration political appointees at the Department of Justice,” Rep. Elijah E. Cummings (D-Md.) wrote in a letter to committee members.

Separately, committee chairman Darrell Issa (R-Calif.) on Tuesday threatened to hold Attorney General Eric H. Holder Jr. in contempt of Congress if he does not turn over documents by Feb. 9. Issa accused Holder’s department of being “actively engaged in a cover-up.”

Republican lawmakers say the department has turned over 80,000 documents to its inspector general, but just 6,000 documents to the committee. In response, a Justice Department official said the department has worked with the committee by providing numerous witnesses and thousands of documents, adding that “we will continue to do so.”

Holder is scheduled to testify before the committee Thursday. At the last hearing, Issa and other Republicans on the committee grilled Holder about Fast and Furious, in which federal agents targeting a drug cartel allowed more than 2,000 guns to flow illegally onto U.S. streets and into Mexico between 2009 and January 2011. Two of the guns connected to the operation were found at a crime scene near Nogales, Ariz., where U.S. Customs and Border Protection agent Brian Terry was slain in December 2010.

Fast and Furious has led to a storm of criticism in the past year from congressional Republicans, many of whom have urged Holder to resign.

The report, called “Fatally Flawed: Five Years of Gunwalking in Arizona,” found that ATF’s Phoenix Field Division launched four “reckless operations” between 2006 and 2010 under both the Obama and George W. Bush administrations and failed to end them even after the flaws became evident.

“Operation Fast and Furious was the fourth in a series of operations in which gunwalking — the non-interdiction of illegally purchased firearms that could and should be seized by law enforcement — occurred since 2006,” Cummings wrote.

The Phoenix division ran “Operation Wide Receiver” out of Tucson in 2006 and ’07, and another 2007 operation called “The Hernandez Case.” The report also details a 2008 operation called “The Medrano Case,” in which ATF agents knew that a man named Alejandro Medrano and his associates were making illegal firearms purchases and trafficking the weapons into Mexico. During that summer, U.S. Immigration and Customs Enforcement agents raised concerns about the tactics, but the operations continued for several more months.

The Medrano case was detailed in a Washington Post series on guns in 2010. But ATF, which promoted the case as a successful gun prosecution, did not reveal in interviews with The Post that federal agents had watched suspects cross the border with guns.

“This report tells the story of how misguided gunwalking operations originated in 2006 as ATF’s Phoenix Field Division devised a strategy to forgo prosecutions against low-level straw purchasers while they attempted to build bigger charges,” Cummings said.

The report also describes the complaints by ATF and agents and officials who said that the situation in Phoenix was compounded by the Arizona U.S. Attorney’s Office, which failed to aggressively prosecute firearms trafficking cases, and the federal courts in Arizona, “which showed leniency toward the trafficking networks that fuel armed violence in Mexico.”

The two Republicans who have led the investigation into Fast and Furious dismissed the findings of the report, with one labeling it a “knee-jerk defense” from Democrats in Congress.

“The idea that senior political appointees have clean hands in these gun-walking scandals doesn’t pass the laugh test,” said Sen. Charles E. Grassley (R-Iowa). “The American people want to see those who failed to act be held accountable.”

Issa called the report’s conclusions a “flawed view that the Justice Department should be given the full benefit of the doubt despite a lengthy record of false statements, misdirection and a continued refusal to turn over subpoenaed evidence.”