This was the big announcement in tonight's 9/11 episode of Jesse Ventura's new
http://www.trutv.com/shows/conspiracy_theory/index.html">truTV show.
Mike Bellone, a Ground Zero rescue worker, told Ventura that he had physically seen one of the black boxes recovered at the WTC and said other rescue workers he was working with said at least 3 were found. Bellone said he was told by the FBI to shut up about finding the black boxes and has been harassed by the Feds. This story about black boxes being found at the WTC was reported first back in
http://web.archive.org/web/20041030023935/http:/www.philly.com/mld/dailynews/news/local/10033802.htm">Oct 2004 by the Philadelphia Daily News.
Bellone was supposed to introduce Ventura to people who apparently worked for American Airlines and were monitoring the calls from Flight 11 and heard some explosive stuff that the government never told the public about, but he said they got scared at the last minute and didn't want to be interviewed anymore. Bellone said they've all been told to hush up by the FBI and one of them is being constantly followed and being bugged by the Feds.
At the end of the show, Ventura said Bellone finally called him later and told him that the reason the government is covering up that they found the black box of the alleged planes that hit the towers
was because those black boxes prove that the hijackers were in the cockpits before the planes took off from the ground and officials at the airports allowed the planes to take off!
It's all hearsay for now of course, but quite the claim!
(The episode should be on youtube soon and I'll post link when up.)