A critical government witness was knocked out of the case of accused embassy bomber Ahmed Khalfan Ghailani yesterday because a federal judge concluded that allowing his testimony would violate the U.S. Constitution.

Dealing a sharp blow to the prosecution, Southern District Judge Lewis A. Kaplan said Hussein Abebe, who allegedly sold Mr. Ghailani the dynamite used in the 1998 bombing of the U.S. embassy in Tanzania, will not be allowed to take the witness stand due to the way he was identified and located through duress—the harsh interrogation of Mr. Ghailani by the CIA.