What are the motifs in Mercy by Jodi Picoult?

Euthanasia is a recurring idea in the story. When the novel opens, Jamie McDonald comes to the Wheelock police station and confesses to the murder of his wife. Jamie says he smothered her with a pillow, because she was suffering from an incurable cancer. Jamie claims that Maggie wanted to die and begged Jamie to do it. However, when Cam interviews Jamie, he cannot help but notice scratches on Jamie's face and hands. Cam wonders why Maggie would fight Jamie if she had wanted him to kill her. Jamie is arrested and put on trial for the murder of his wife.