Firstly, my condolences to Lee Rigby's family. What a tragic waste to have a young life cut short with such barbarity.
Secondly, I assume Basil was writing about the tragic death of school boy Damilola Taylor. I think that people remember his death for the same reason that they will Lee Rigby's ie a heinous murder committed by people filled with a senseless hatred.
As for Britain's multicultural population I think it says something good about the innate British tolerance and respect for others. Something to celebrate not condemn. Whether large scale immigration was beneficial to the UK is something best debated, IMHO, by considering the broader aspects and not an isolated and barbaric act.