Ratted out, tipped off, narced, spilled the beans, snitched, let it slip
Ratted out - to inform an authority figure (usually police) about illegal activity. Usually used to describe the revealing of all secrets in detail; full disclosure.
He ratted them out to the police.
Frank ratted me out to the cops, he's nothing but a rat!
I'm going to rat out Frank.
Tipped off - to inform someone of something without others knowing. Usually used to describe only a single piece of information (a tip) being revealed. Could be used to denote revealing information anonymously.
He tipped off the police to their location.
Someone must have tipped them off.
My buddy tipped me off about an investment opportunity.
Narc - to inform an authority figure (usually police) about illegal activity, or used to describe someone who agrees to work with the police. Comes from the word narcotics and is usually used with drug related crime.
I'm going to narc on Frank.
Frank narced us all out.
Frank is a narc.
Spilled the beans - used to describe the revealing of all secrets in detail; full disclosure. Not specific to malfeasant behavior.
Frank spilled the beans about our operation.
I'm warning you not to spill the beans about this.
Snitch - to inform an authority figure (usually police) about illegal activity, or used to describe someone who agrees to work with the police.
Frank is a snitch.
Frank snitched on us!
Snitches get stitches. - Used to convey a warning that if you reveal the secret
you will be physically harmed.
Let it slip - to reveal a secret. Usually used to describe only a single piece of information being revealed. Often used to denote revealing information accidentally. Not specific to malfeasant behavior.
Frank let it slip that we were there.
Try not to let our plans slip this time.
Tell on - to inform an authority figure (usually a parent, teacher, or boss) about someone's bad behavior. Similar use to the word "tattle".
I saw what you did Frank, I'm going to tell on you.
Frank told on me to the teacher.