An award-winning Iranian nuclear scientist, who disappeared last year under mysterious circumstances, has defected to the CIA and been resettled in the United States, according to people briefed on the operation by intelligence officials.

"The significance of the coup will depend on how much the scientist knew in the compartmentalized Iranian nuclear program," said former White House counter-terrorism official Richard Clarke, an ABC News consultant.
EXCLUSIVE: Iran Nuclear Scientist Defects to U.S. In CIA 'Intelligence Coup' - ABC News