The Journalist and the Murderer, by Janet Malcolm
That searing opening paragraph. That excoriating criticism of Joe McGinniss's methods where he gained access to Jeffrey Macdonald, presumed killer of his wife and children, by professing belief in his innocence only to turn on him in print. But I've always thought Malcolm's brilliant, merciless 1989 book didn't really care much about the Macdonald case – it was just a perfect, legally fraught example of the failures of the journalist-subject relationship. And it's why I return to it again and again with different journalist-murderer cases well in mind.