An attorney for Sylvia Ash, the state Supreme Court judge accused of obstructing an investigation into the state-chartered credit union whose board she used to chair, said Monday that key evidence against her client had been obtained in violation of her Fifth Amendment protections against self-incrimination.

Carrie Cohen, a Morrison & Foerster partner who is representing Ash in the criminal obstruction case, argued in a court filing that Municipal Credit Union was effectively acting on behalf of federal prosecutors when it told the embattled judge in June 2018 to return the iPhoneX its chief executive had issued her just months before.