squeal on (one)
To inform a figure of authority about someone else's crime, wrongdoing, or transgression. I'm afraid the mafia will make a hit on me since I squealed on them to the police about their money-laundering operation. Why would you squeal on me to the teacher like that? Don't tell your sister anything, she'll squeal on us the first chance she gets.
To disclose incriminating information about someone: The accountant squealed on her corrupt managers. He squealed on his brother for jumping on the bed.