FREEPORT – David D. Gregory, a law professor who helped oversee state compliance with a federal court order governing rights of residents of a state institution for the mentally retarded, died Saturday of cancer. He was 59.

Gregory taught at the University of Maine School of Law since 1972, where four years earlier he received his law degree. He was co-author of the treatise “Maine Tort Law.”

A Rockland native, Gregory attended Princeton Theological Seminary before pursuing a law degree.

Since 1984, he was counsel to the York County District Attorney’s Office, assisting on criminal case appeals.

From 1978 to 1983, he was executive secretary to the Committee on Judicial Responsibility and Disability, the ethics panel established by the Maine Supreme Judicial Court to conduct investigations and disciplinary proceedings against state judges.

The U.S. District Court appointed Gregory in 1978 as special master to ensure state compliance with the Pineland consent decree governing rights of residents of the Pineland Center, a post he held until 1981.

He was counsel to the National Association for the Advancement of Colored People from 1972 to 1978, where he prepared briefs for submission to federal appeals courts in school desegregation cases.

From 1968 to 1971, he was a trial and appellate attorney for the Civil Rights Division of the U.S. Department of Justice in Washington, D.C.

Gregory’s survivors include his mother, Louise Dolliver Gregory of Owls Head; his wife, Jane Backlund Gregory of Freeport; his twin brother, Donald, of Boston; and two daughters from a previous marriage.

A private service will be held for the family. The University of Maine School of Law will hold a memorial service in January.