The third time is enemy action, asserts the old Intelligence Community saying.
A British nuclear expert taking part in disarmament talks with Iran has died in mysterious circumstances at a UN building in Austria.
Timothy Hampton, 47, plunged to his death from the 17th floor and was found in a stairwell just hours before high-level discussions were due to resume in Vienna.
Investigators said they have not ruled out murder or suicide, but local sources said no suicide note was found.
Police are also investigating the death of another Brit who fell from the same building four months ago.
The third such incident will be very hard to take for just another accident.