Never speak ill of the dead

I write quite a lot of funeral eulogies and it occurs to me that they are generally very good examples of how we always try hard not to speak ill of the dead. You will have noticed that when someone dies they are invariably described as 'one of the nicest, kindest, most thoughtful, unselfish, generous people you could ever hope to meet.' Now I don't want to sound cynical but of course not all people are like that. What will I say if I'm asked to write about an infamous serial killer who lead a life of indescribable evil and depravity? I'll worry about that if and when it happens!