Because someone is dead doesn't mean they're gone.

Gothika

After a car crash, criminal psychologist Dr. Miranda Grey regains consciousness only to find that she's a patient in the same mental institution that currently employs her. She's been accused of murdering her husband Dr. Douglas Grey — but she has no memory of committing the crime. As she tries to regain her memory and convince her co-worker, Dr. Pete Graham, of her innocence, a vengeful spirit uses her as an earthly pawn, which further convinces everyone of her guilt.