We need to distinguish between freelance lawyers and public (court-appointed) defenders. The first can say "no, I am not interested in defending you", because there are always public lawyers.All murderers have barristers defending them in the UK. I suspect most of them know that they are guilty. But they are still required to defend them.
By the way...I won't judge them...it's just that you need to be an atheist to do such a thing in my humble opinion.