On a sweltering August afternoon in 1991, three dark-haired men approached an ivy-covered villa in the Paris suburb of Suresnes. It was the home of Shahpour Bakhtiar, 76, exiled former Prime Minister of Iran and a leader of the anti- Khomeini opposition. Since fleeing Tehran in 1979, Bakhtiar had been one of the most closely guarded men in France, watched over by paramilitary police 24 hours a day.
The arrival of the three men raised no alarm, since one was Farydoun Boyerahmadi, 38, a Bakhtiar aide and confidant. He was bringing two friends, Ali Vakili Rad, 32, and Mohammed Azadi, 31,...