The official record states that senator Robert F Kennedy, like his brother before him, was killed by a crazed lone gunman. But the assassination of a man who seemed to embody so much hope for a bitterly divided country embroiled in an unpopular war still troubles this nation.

Little about the official explanation of the events at the Ambassador Hotel on June 5 1968 makes sense. Now a new forensic analysis of the only audio recording of the fatal shots has given new weight to a controversial theory that there were in fact two shooters, and that the man convicted of Kennedy’s killing — Sirhan Sirhan - did not fire the fatal shots.