Khalid Sheikh Mohammed, mastermind of the 9/11 attacks on America, built a vacuum cleaner in the basement of a CIA secret prison in Romania where he was confined.  Mohammed has a degree in mechanical engineering. (ETA: he built schematics for a vacuum cleaner.)

The agency officer in charge of the prison called CIA headquarters and a manager approved the request, a former senior CIA official told The Associated Press.

KSM had undergone severe interrogations but eventually his usefulness as an information source ran out. 

“We didn’t want them to go nuts,” the former senior CIA official said, one of several who spoke on condition of anonymity because they were not authorized to talk about the now-shuttered CIA prisons or Mohammed’s interest in vacuums.

Using schematics from the internet, KSM undertook his new project producing the world’s “most highly classified vacuum cleaner.”

KSM was imprisoned along with other Al Qaeda terrorists, Ramzi Binalshibh and Abd al-Nashiri.  The interrogation methods used by the CIA usually results in some degree of psychological damage.  Both Al-Nashri and Binalshibh are suffering from mental issues. The CIA had a challenge to keep these prisoners occupied, even giving them books to read. KSM was a fan of the Harry Potter series. 

The prison had a debriefing room, where Mohammed, who saw himself as something of a professor, held “office hours,” as he told CIA officers. While chained to the floor, Mohammed would lecture the CIA officers on his path to jihad, his childhood and family. Tea and cookies were served.

KSM’s lawyer was prohibited from discussing the vacuum cleaner. “It sounds ridiculous, but answering this question, or confirming or denying the very existence of a vacuum cleaner design, a Swiffer design, or even a design for a better hand towel would apparently expose the U.S. government and its citizens to exceptionally grave danger,” [Jason] Wright said.

The CIA will not discuss KSM’s vacuum.  Associated Press’s FOIA request on the topic received a response indicating that “should they exist” the plans would be considered operational files of the CIA, the most classified category of government files, and are exempt from public release.