More than 250 of America's most eminent legal scholars have signed a letter protesting against the treatment in military prison of the alleged WikiLeaks source Bradley Manning, contesting that his degrading and inhumane conditions" are illegal, unconstitutional and could even amount to torture. The list of signatories includes Laurence Tribe, a Harvard professor who is considered to be America's foremost liberal authority on constitutional law. He told the Guardian he signed the letter because Manning appeared to have been treated in a way that "is not only shameful but unconstitutional" as he awaits court martial in Quantico marine base in Virginia. Under the terms of his detention, he is kept in solitary confinement for 23 hours a day, checked every five minutes under a so-called "prevention of injury order" and stripped naked at night apart from a smock. Tribe said the treatment was objectionable "in the way it violates his person and his liberty without due process of law and in the way it administers cruel and unusual punishment of a sort that cannot be constitutionally inflicted even upon someone convicted of terrible offences, not to mention someone merely accused of such offences". The harsh restrictions have been denounced by a raft of human rights groups, including Amnesty International, and are being investigated by the United Nations' rapporteur on torture.