An FBI informant who has helped catch some of the world's most dangerous terrorists is coming out of witness protection to warn that a terrorist sheik in prison remains a significant threat to the U.S., according to NBC 4 New York. Emad Salem is urging the U.S. to keep the ailing 74-year-old sheik Omar Abdel Rahman behind bars and to not transfer him, even as governments overseas continue to press for his release. "He will kill Americans," said Salem. "He will kill anyone who disputes what he says with a fatwa." Salem, a one-time Egyptian military officer, had warned officials about the looming 1993 World Trade Center bombing, but his warnings were ignored after a lie detector test was inconclusive and he said he would never testify at any trial. After the bombing, Salem agreed to become an FBI informant and managed to become the sheik’s personal assistant and bodyguard. Salem was also able to link the sheik to the 1993 World Trade Center bombers. Now Salem is concerned about the mounting pressure on the U.S. from Egyptian President Mohammed Morsi and other Mideastern government leaders to get Rahman out of American custody.