Terrence O'Donoghue

SPOILERS!!!!!

I must have missed this, but how did Terrence O'Donoghue know about the paintings on Amber's bedroom wall? Despite the fact that they showed her dead in his car, I think that was not supposed to be what really happened but a product of his mind. Or was it? It was said that he was in custody at the time of Amber's disappearance. So how on earth did he know about her paintings?????