I know of 2 different conspiracy theories and I was hoping for clarification.
The one theory is that all political leaders (Ali, Muawiya and Amr bin Aas) were to be assassinated to clear the political fighting in Medina. This would explain the events you mentioned in your last sentence.
The other says it was Muawiya alone who was behind it and had lured people in with false promises and the other attempts were just for show.
And then of course it could be possible that it was the act of revenge for the leniency of not sufficiently punishing the killers of Uthman in 656.
Any substantiated opinion?