Updated

A U.N. human rights expert on torture is urging U.S. authorities to end four decades of solitary confinement for a former Black Panther convicted of murdering a Louisiana prison guard.

U.N. special rapporteur Juan Mendez said Monday the indefinite solitary confinement imposed on Albert Woodfox "clearly amounts to torture and it should be lifted immediately."

Woodfox, 66, and fellow prisoner Herman Wallace were serving unrelated sentences for armed robbery in 1972, when they were charged and convicted with fatally stabbing a guard.

The two men, who helped establish a Black Panther prison chapter, were moved to isolation in Louisiana State Penitentiary at Angola, then to "closed-cell restriction" at other state jails.

Wallace died Friday at 71, only days after a federal judge ordered a new trial for him.