IMMUNITY

When only circumstantial evidence is available in a suspected espionage case and there is little prospect of a conviction at a criminal trial, a formal immunity from prosecution may be negotiated to extract an intelligence advantage from an individual thought to possess potentially valuable information. Occasionally considered controversial because the procedure may allow a self-confessed spy to go unpunished, it does offer the opportunity to exercise some leverage on an otherwise unpromising case. Such cases are rarely publicized, although the immunity offered to Kim Philby in January 1963 and to Anthony Blunt in April 1964 eventually was disclosed.