It's something blues cite now but I doubt it was that.
It was.
Prior to Heysel we always knew that, though they were in the ascendancy from the mid seventies through the mid eighties, we would turn things round.
And we had by 1985, when Everton's time had come.
Then Heysel happened and Everton, along with United and others, found thenselves banned from Europe through no fault of their own.
There was a daft midweek competition set up for the clubs banned from Europe called the Screen Sport Cup (Screen Sport was a satellite sports channel, a forerunner of Sky and BSB).
It featured Everton, Liverpool, United and Norwich City, who had won the Milk or Rumbelows or Littlewoods or whatever Cup that year.
We played Liverpool in the two legged "semi final" and they started taunting us about not playing in the European Cup.
(that Steaua Bucharaet banner is part of the same Kopite mindset)
Anyway, we started chanting "Murderers, murderers" at them and from that day on I detected a nastiness creeping in on derby day.
Just my own opinion, of course.