Original sentence: One, strongly advocated since the early 1980s by Michael Ledeen among others, is that the assassination attempt had originated from Moscow and that the KGB instructed the Bulgarian and East German secret services to carry out the mission
Edited sentence: One, strongly advocated since the early 1980s by Michael Ledeen among others, and the most widely accepted scenario, is that the assassination attempt had originated from Moscow and that the KGB instructed the Bulgarian and East German secret services to carry out the mission