Mossadegh?? Shit, anyone who has studied that region at all knows about Operation Ajax, where the CIA helped remove Mossadegh from power. But that was in 1953, and Mossaddegh died in 1967 - 14 years later at the age of 85.
I've honestly never heard anyone even allege that Mossadegh's death was actually a CIA assassination, though. That's a new one on me, so I'd need to see a link or something on that because it makes no sense. Why would the CIA assassinate an 85 year old man who'd been out of power for more than 13 years? The Shah was firmly in control by that point, and if he wanted Mossadegh's dead, he'd have just gotten SAVAK to do it. Is this something Seymour Hersh has started claiming?
But honestly, I've never read anything claiming Mossadegh's death was due to anything other than natural causes. I mean, he was 85. So why the fuck would LBJ have ordered his assassination at all?