He was convicted earlier Friday for taking the girl during a supervised visit and for assaulting the social worker who was with them.
Rockefeller's real name is Christian Karl Gerhartsreiter. He snatched the girl on a Boston street last July and fled to Baltimore with her.
Jurors on Friday rejected the claim by defense lawyers that he was suffering from a delusional disorder and was legally insane. Prosecutors say he planned the kidnapping for months after losing custody of the girl in a divorce.