Here's a recent indepth interview on this topic, with GE himself.
I remember watching this with my LR-style running buds. It was immediately evident that Evangelisti had not broken 8m on his final effort and wasn't in the same zipcode as Myricks. He was puzzled himself, walking back to the measuring board behind the pit and clearly not comprehending how it was so long.
There has never been any belief that he was directly involved in this but the scandal did feature the backdoor puppets of PRIMO fixing the measurement. What was astonishing was not Primo's malfeasance or the plan, but that they had the chutzpah to do this in front of dozens of millions even then watching on live TV who could see from their seats the brazen false measurement. And it wasn't like a 5cm overage - his jump was a handspan under 8m, but he was credited with 8.38m, so almost 50cm extra...gratuitous indeed.
Prior to that, I never believed such blatant cheating was thinkable in a televised major world event but seeing this changed the way I thought about T&F. It certainly lent additional weight to Fred's infamous pronouncements from his villa on the hilltop that same week... "People have come out of nowhere and are running astonishingly..." etc.