WASHINGTON — Penn State University faculty member Jonathan H. Marks wants interrogation documents that the Pentagon insists on locking up.The resulting struggle over sensitive information, now entering its seventh year, has become an unexpected master class in government secrecy for the Oxford-educated Marks. Hoping to shed light on harsh U.S. interrogation techniques, he has simultaneously undertaken a long and instructive legal journey.[…]The long fight for government documents has cast Marks, a 44-year-old associate professor of bioethics, humanities and law, into a wilderness only partially penetrated by the Freedom of Information Act. Others know similar terrain well. Federal information, it turns out, is not always free.