US government officials supported secret negotiations aimed at securing the release of American hostage Abdul-Rahman Peter Kassig, who was abducted and eventually murdered by Islamic State. Emails seen by the Guardian show how tentative talks between US lawyer Stanley Cohen, former Guantánamo Bay detainees, jihadi scholars and Isis's spiritual elite ran for several weeks before coming to an abrupt end when Jordanian security services arrested scholar Abu Muhammed al-Maqdisi, who was at the heart of the negotiations