JOIN USManfred Nowak, the UN's special rapporteur on torture, told the BBC that such a duty existed even if the alleged human rights violations dated back to a previous government.
"President Obama also has an obligation to deal with past cases," said Nowak. "There is an obligation to investigate whenever there are credible allegations torture has happened - and these allegations are more than credible - and then it is up to the courts."
There should initially be an "independent and objective investigation", said Nowak. After that, it would be up to the courts on the one hand to bring the perpetrators to justice and also on the other hand to provide the victims with adequate reparation for the harm they have suffered.
Nowak's comments related to allegations that US officials and the military turned a blind eye to torture by Iraqi soldiers on fellow-Iraqis.