The McBride enquiry is now only on Jstor, a subscribers only site, as far as I can make out – a couple of years ago it was freely on-line.
In 1983, a commission chaired by Seán MacBride, the assistant to the UN Secretary General and President of United Nations General Assembly at the time, concluded thatIsrael, as the camp's occupying power, bore responsibility for the violence.[19] The commission also concluded that the massacre was a form of genocide
A few of interesting links here:
Permission to Narrate

Action Alert Archives

A preventable massacre

Israel misled and bullied U.S.

Israel's systematic harassment of US Marines

Jim Carroll