Fender - // ... why lawyers take on such cases is beyond me, must the money... //
I think you'll find it's more a case of a belief in the legal system being operated correctly.
For a civilised society to run a proper system of law with the correct checks and balances, it must mean that everyone has the right to a fair trial, and that must include the best defence available.
Only if a proper defence has been mounted, and then the defendant been found guilty, can the society be sure that justice has been served.
I believe that lawyers who defend criminals are motivated by that need to provide a proper legal system that means justice can be just that - just.