From Longman Business Dictionary
investigatein·ves·ti·gate /ɪnˈvestɪgeɪt/ verb [intransitiveI, transitiveT] to try to discover the truth about a crime, accident etcThe fraud office isinvestigating allegations of insider trading by a former employee of the firm.
—investigation noun [countableC, uncountableU]a bankerunder criminal investigation
a federal investigation into junk bond trading
—investigator noun [countableC]a government investigator