When the chairman and chief executive of Total SA, Christophe de Margerie, was killed this week after his private jet hit a snow-removal truck on takeoff from a Moscow airport, it looked like an accident.

Russian television viewers were treated to a different version. According to a top Russian television channel, a plot by the Central Intelligence Agency couldn’t be ruled out. Mr. de Margerie was, after all, a prominent opponent of U.S. and European Union sanctions on Moscow, and Washington wanted him silenced. This story...