Two US prisoners who have been held in solitary confinement for nearly 40 years should have their isolation ended immediately, Amnesty International said Tuesday. Albert Woodfox, 64, and Herman Wallace, 69, have been held in solitary at Louisiana State Penitentiary ever since they were convicted of murdering a prison guard in 1972, the London-based human rights group said. Their four-decade ordeal "is cruel and inhumane and a violation of the US's obligations under international law," said Guadalupe Marengo, Amnesty's Americas deputy director.