There is no affirmative obligation to report fraud or any crime: person A  has no duty to report the crimes of person B. Mere knowledge does not make you an accomplice; however, doing something to further the fraud or other crime does make you an accomplice. So you are not liable (either criminally or civilly) for this, but the partner would be, if they "know they lied on their claim"--the act of lying (as opposed to merely standing silent on the subject, as you are) would make them liable.IF anyone does ask you about this--e.g. an insurance investigator; a prosecutor; etc.--you have to answer honestly: you don't have to volunteer information, but lying could again make you liable.