The man long-considered the most responsible for the September 11 terrorist attacks has been in prison a long time—so long that he appears to have had time to reinvent common household appliances. A new report from the Associated Press claims that Khalid Sheikh Mohammed, who was captured by the CIA in 2003, was allowed to spend of his free time working on designs for a new vacuum cleaner.

CIA officials says Mohammed was allowed to indulge his hobby — he actually has a degree in mechanical engineering from a North Carolina university — both as a reward for good behavior and to keep him sane. They were concerned that his long imprisonment might do so much psychological damage that he would no longer be useful as source for information. (Other detainees have experienced severe mental breakdowns as result of their torture and long confinement.) The terrorist leader had already been tortured numerous times while being held in secret "black site" prisons in Eastern Europe, and his value as a prisoner had been mostly exhausted. But agents also knew he wasn't going to be released anytime soon and he might helpful again in the future, if he stayed healthy.

The "project" was one of many designed to keep prisoners like Mohammed lucid and cooperative. According to the same CIA sources, he would often hold "office hours" with CIA officers, where he would lecture them about Islam and his history of jihad. He also liked to read books, including the Harry Potter series.

The officials say they considered the possibility that the vacuum designs were just a ruse to trick interrogators or pass messages to other prisoners or the outside world. No one knows what happened to his actual blueprints, however. The AP's attempt to obtain them through a Freedom of Information Act request was denied on the grounds that they are now classified CIA materials. Mohammed is currently in Guantanamo Bay, Cuba, where he is still being tried in a years-long military tribunal.

Image credits: Court sketch: AP Photo/Janet Hamlin; Vacuum: steamroller_blues via Shutterstock