Law professor and author Arthur Miller, appearing as an expert in civil procedure Thursday, agreed with the National Rifle Association’s argument that the New York Attorney General’s Office cannot prevent the gun-rights group from reviewing potentially privileged material in the possession of its former advertising agency Ackerman McQueen, which has received a state subpoena.

The subpoena is related to the Attorney General’s Office’s ongoing investigation into the NRA and its financial affairs, which was publicly confirmed in April.