Remember the Mavi Marmara? The ship, one of six sailing from Turkey to Gaza in May of 2010, was piloted by activists from IHH, a Turkish radical Islamist group that several countries, including Israel, classify as a terrorist organization. Masquerading as human rights activists carrying supplies to Gaza, the ship defied Israel’s naval blockade of the Hamas-controlled strip, eager to generate a global controversy. It did just that: As Israel Defense Forces soldiers took over the vessel, a violent altercation ensued, leaving nine IHH members dead and 20 wounded.

Just what happened on board the ship? For years, Israel had insisted that shots were only fired after one of the Mavi Marmara’s passengers had managed to seize the weapon of an IDF soldier, putting the soldier in mortal danger. This version was widely disputed by pro-Palestinian advocates, who argued that the Israeli soldiers opened fire indiscriminately, slaughtering the civilians on board with little provocation.

But in newly revealed posts from Palestine Live, a secret British Facebook pro-Palestinian group, Greta Berlin, the co-founder and spokesperson of the Free Gaza Movement, confirmed Israel’s account and admitted that the IDF soldiers opened fire only after an American activist named Ken O’Keefe approached one of the them and violently managed to disarm him.

O’Keefe, Berlin wrote in the private forum in 2014, “was responsible for some of the deaths on board the Mavi Marmara. Had he not disarmed an Israeli terrorist soldier, they would not have started to fire. That’s enough. Most of you have no idea what you’re talking about.”

Indeed. The posts were uncovered by blogger David Collier, who infiltrated the invitation-only online group and outed Labour leader Jeremy Corbyn as one of its members.