A government investigation has found that one-third of the Federal Bureau of Investigation’s entire aviation budget between 2008 and 2012 was spent on executive transportation, including travel by attorneys general, FBI directors and other top bureau officials, according to a new report released Monday. The report found that in 2009, 33 percent of flights taken that year were for executive transportation. In 2012, 34 percent of aircraft use was for executive travel.

Ashed where executive transportation ranked on the “priority list” for airplane use, the bureau said such travel requests were “secondary.” “Investigative/operational missions are the FBI's highest priority, followed by required maintenance and pilot training missions,” the bureau said in the report. The bureau added that the “FBI pays for the cost of operating aircraft flown by the attorney general as part of its mission to protect him.” The bureau also said executive travel had never interfered with any operational flights.

Former Attorney General Eric Holder and former FBI Director Robert Mueller were among the Department of Justice officials who have used the FBI’s aircraft for business or personal travel. Between 2007 and 2011, Holder and Mueller, as well as then-Attorneys General Michael Mukasey and Alberto Gonzales, took nearly 700 trips not related to bureau intelligence operations, according to a previous government report. The trips' cost totaled roughly $11.4 million. In some cases, officials reimbursed the government for a portion of the expenses.

Holder has previously defended using the justice department’s plane for personal trips. “We didn’t have a reporting requirement that existed before,” Holder said during a House Appropriations Committee hearing in 2014 when asked whether he would report those trips to the General Services Administration in the future. “If they want to change those rules, we’d be more than glad to make sure that we share that information with the appropriate organization, but this is something that is really wide open.”

FBI officials’ use of the bureau’s private planes for business or personal travel came to light in 2013, but exactly what percentage of the bureau’s aviation budget went toward executive transportation was unclear.