A Central Intelligence Agency officer who allegedly threatened a detainee with a gun during an interrogation in 2002 has been officially "reprimanded and reassigned" for using tactics outside the agency's legal guidelines.

The punishment is part of the early fallout as the CIA prepares to release a long-secret internal report Monday detailing the use of a mock execution and threatening detainees with power drills and guns during interrogation.

Originally written in 2004, but only shown to select US government officials and upper-level CIA officials, the report will be released on Monday following a federal judge's decision to uphold an appeal by the American Civil Liberties Union, reports The New York Times.

Some of the most graphic methods described in the report were used on Abd al-Rahim al-Nashiri, who allegedly planned the 2000 USS Cole bombing. According to the report, CIA officials fired a gun in an adjacent interrogation room to make Mr. al-Nashiri think another prisoner had been executed. In addition to waterboarding him, interrogators also turned a power drill on and off next to his head, reports Newsweek, which first broke the story. A federal law prohibits authorities from threatening prisoners with "imminent death."

These recent developments of potential CIA misconduct during interrogations come as the agency is already facing increasing scrutiny. US attorney general, Eric Holder, is currently reviewing the legality of CIA interrogation methods, reports the Guardian.

The report is understood to be the most detailed review of the agency's interrogation program and is believed to be highly critical of the techniques used, suggesting that a number of them broke international laws and norms. The document has become deeply controversial within the CIA itself, not least because the agency was advised two months before Nashiri's capture in a memo from Jay Bybee, the head of the justice department's office of legal counsel, that threats of "imminent death" were legal if they did not cause permanent mental harm.

Taking legal action against those involved in questionable interrogation procedures may be difficult, reports The Washington Post. Although Justice Department lawyers reviewed the case, they declined to press charges. A. John Radsan, a former assistant general counsel at the CIA, told The Post that cases like this present unique challenges.

"The victims are not sympathetic. Witnesses may not talk. Evidence may be gone," Radsan said. "If anyone is indicted, there will be the usual graymail. The defendant is going to push [Justice] to reveal things about the program that will even make this administration uncomfortable. The defendant will say whatever he did was reasonable reliance on advice from government lawyers."

The incidents described in the report are among the most extreme examples of "enhanced interrogation" techniques used by CIA interrogators. While waterboarding and sleep deprivation were approved in legal memos from the Justice Department, other methods, such as using a power drill appear to have been improvised methods not specifically mentioned by the Justice Department. One former US official described some of these practices to The Los Angeles Times as being done "almost in juvenile detective mode."