be onto somebody
From Longman Dictionary of Contemporary Englishbe onto somebodybe onto somebodyinformal a) (also get onto somebody especially British English) to speak to someone in order to tell them or ask them something A number of people have been onto me complaining about the noise. Get onto the Press Office and find out what’s happening. b) to know that a particular person did something wrong or committed a crime The police are onto him. → ontoExamples from the Corpusbe onto somebody• He's scared. He knows we're onto him.