|Canon 983: The sacramental seal is inviolable; therefore, it is a crime for a confessor in any way to betray a penitent by word or in any other manner or for any reason.|
"In any way" "in any manner" "for any reason" seems to indicate that even if the priest suspects that the person is not truly repentant, he still can't violate the sacramental seal.
There was a recent case where a priest I slightly know, was actually arrested because a computer owned by him had child pornography on it. When questioned about it his answers sounded disturbingly evasive, even to me. Later turned out that a grad student had put the porn on the priest's computer (which was in a common area), and had confessed it.
The priest faced a total sliming of his good name, suspension from the priesthood, loss of his job at the University, and criminal prosecution, and yet could not even indirectly allude to the fact that somebody had confessed that he'd put this crap on the computer.
He was later totally exonerated when the offender of his own volition went to the police and confessed.
A dramatic case. You could probably find it if you google the priest's name, Fr. Mark Gruber.