Choosing names for characters in a crime novel

What's in a name? An awful lot as far as an author is concerned. Getting the right name for the characters in my crime novels can be a tricky business. Sometimes they can come to me completely out of the blue, other times I will struggle to find the name that best suits that particular character and until I do the personality refuses to come alive. The name also needs to fit with the age and nationality of that character although you can have exceptions.