Who is really guilty?

Briony spends her entire life trying to atone for accusing Robbie of a crime he didn't commit and for ruining Robbie's and Ceceila's chance for love and happiness. She certainly feels guilty, but is she really responsible for this crime of was her crime unintentional and not premeditated? Briony was a victim of her own imagination. As a precocious child immersed in literature and fairy tales, she constructed her world according to the fiction she read. Order was achieved through a set of black and white rules and life had to fit that framework. In Briony's world, there was the princess stolen away by the evil "maniac," and the prince who saves the princess from an evil fate (after he saves her from drowning). Thus, when Briony inadvertently sees Ceceila and Robbie at the fountain, she can only interpret the scenario in one way as she forces the scenario to fit into her view of the world which she has created through the stories she has read. She knows no better and should not be expected to know better. But when events do not unfold as she expected (ie. Ceceila being rescued from the fountain, followed by a proposal), and when she reads Robbie's sexually explicit note, she can only now cast Robbie into the role of the evil "maniac," a role she feels was always his and that she had just missed the signs. So even though Briony thought that " for now it could no longer be fairy tale castles and princesses, but that her writing had now matured to a new level - that she had "privileged access across the years to adult behavior," she is still a child and still forcing what she sees in the world according to the princesses and bad guys. Her actions are also motivated by her own desire to write. Briony is so convinced that Robbie is the evil maniac, she feels she must protect her sister. However, she is a victim of her background of fiction and thus it was so "easy to get everything wrong." It is easy to convince herself that Lola's attacker was Robbie and as a child, it was hard once the investigations intensified to extricate herself from her accusations. Once she was able to realize what she had done, her guilt is so overwhelming that she pends the rest of her life trying to atone for her crime by the only way she really knows how - by writing the story of what happened, specifically writing the story "from three points of view...to show separate minds, as alive as her own," to suffer by understanding exactly what Robbie and Ceceila felt and went through because of her. Writing has caused Briony to lie, and writing is the only way she knows how to atone for her sin. But even her writing must be falsified to make her achieve her goal.
(As an aside, I think it is interesting that McEwan has chosen to contrive his own writing of the story to help reinforce Briony's views of Robbie as a monster. When Robbie emerges from the woods with the twins, he appears as if he were a gigantic monster because he has one of the twins on his shoulders. This depiction again reinforces for Briony that Robbie must me the evil one who committed the crime and MCEwan by describing Robbie that way forces him into that role.)
But who should really be guilty in this novel? Commenting on the social evils of the time, McEwan, through Emily Tallis and both Lola and Marshall, reveals the ills of class superiority in England. Emily Tallis is perfectly content to see Robbie accused of the crime and is blinded by her own prejudices of her superiority over the gardener's son. She has always resented that her husband paid for Robbie's education and snobbishly comments that it was a fancy of her husband. In the last section, McEwan paints Lola as a Cruella DeVille "the guant figure, the black coat, the lurid lips." Although Lola and Marshall are huge philanthropists, Briony comments that perhaps he has given away so much money "spending a life time trying to make amends." But the other option that Briony suggests is most like the truth - "or perhaps he just swept onward without a thought, to live the life that was always his." The Marshalls are definitely guilty of the crime, but because of their place in society, they will be protected.
Although Ceceila is cast as a victim, she too in reality, cannot escape her own notions of class and is convinced that the gardener Danny was guilty.