Oh, I wrote my bachelor's thesis about this. Well, about the Kahan commission. The Kahan commission was an Israeli commission, led by several Israeli judges, who were tasked in finding out exactly that - what happened at Sabra and Shatila and how much blame falls on Israel. The conclusion of the report was clear: the Phalangists were directly responsible for the massacre, Israel was indirectly responsible and Ariel Sharon had a personal responsibility. It was seen as a bold and impressive move by the international community - a nation that looked to recognise its own mistakes and responsibilities, an exercise in democracy.
The problem, however, is that the Kahan commission was - despite its unprecedented admission of guilt from Israel - a whitewash. Well, not a total whitewash, since it did lay some blame at the feet of Israel and Sharon, something that was fairly unprecedented at that point. But it was hard to deny those facts - even if you believed the most hardline Israeli version of the events, they'd still carry that responsibility because it happened in territory occupied by the Israeli's. The Kahan commission was a whitewash, however, because while it was undeniably the Phalangists carrying out the massacres, Israel - and Sharon - played an active part in making it happen and can't get away with just an admission of "indirect responsibility".
The short version of what happened, then. Two months after Israel invaded Lebanon, a deal was struck after mediation by the international community. The PLO fighters and Syrian troops would get free passage to evacuate from West Beirut. All was going well, until the assassination of the recently elected Christian president of Lebanon, Bashir Gemayel, on 14 September. The very next day, the IDF invaded West Beirut. By the 16th, the entirety of West Beirut was under Israeli control, having met little resistance after the evacuation. The IDF surrounded the Sabra and Shatila refugee camps. Israel's allies in the war, the Christian Phalangists under command of Elie Hobeika, were sent into the camps under orders to remove any remaining PLO fighters. During the next three days, between 700 and 3000 Palestinian refugees were massacred under the eyes of the IDF.
While the IDF later claimed they knew nothing of what happened and were powerless to stop it, even while the massacres were ongoing, the international press managed to catch wind of it. What followed was a storm of protest and outrage, even in Israel itself. At first, the Israeli government wasn't prepared to budge - they did nothing wrong, they claimed. In the words of prime minister Begin: 'Goyim are killing Goyim. Are we supposed to be hanged for that?' This position became untenable once 300.000 to 400.000 Israeli's came out onto the streets in protest. The pressure, both internal and international, was insurmountable and by the end of September the Kahan commission was born.
The Kahan commission - officially the "Commission of Inquiry into the events at the refugee camps in Beirut" - was named after its chairman and then president of the Israeli High Court, Yitzhak Kahan. Along with another high court judge, Aharon Barak, and Major-General of the IDF, Yona Efrat, they were tasked in finding out what happened. In their conclusions, they lay the blame at the feet of the Phalangists. Israel and the IDF could not have foreseen the massacre, let alone stop it. They held an indirect responsibility. Then minister of Defence Ariel Sharon and a few military men (including Chief of Staff Rafael Eitan and director of Military Intelligence Yehoshua Saguy) were held personally responsible. As a result of this, despite his initial refusal to do so, Sharon left his post as minister of defence, yet stayed on as minister without portfolio. Saguy was fired and Brigadier-General Amos Yaron was suspended from leadership positions within the IDF for three years.
Despite loud praise coming from Israel's allied governments in the West, there was a lot of criticism too. I'll keep these fairly short, but feel free to ask for more information. The commission was criticised for the following:
a) Ignoring witness statements it declared to be biased, such as the testimony of the Jewish-American nurse Ellen Siegel who was present at the camps at the time of the massacre and was about the presence of Israeli soldiers. Meanwhile, Israeli soldiers and officers' testimonies were accepted without question.
b) Assuming the presence of PLO fighters in the refugee camps. This was one of the major criticisms on the facts mentioned in the report. The IDF claimed that the PLO didn't keep their part of the evacuation deal and left a large contingent of fighters in West Beirut, including 2.000 fighters in Sabra and Shatila. No source is given for this claim, except press releases of the Israeli government. More damningly, the IDF claims the massacre resulted in 700-800 casualties - but what happened to the other 1200-1300 fighters then? And seeing as many of the casualties were women and children, how is this explained? Moreover, in the immediate aftermath of the takeover of West-Beirut, the Chief of Staff described the area as "quiet". An intelligence officer was quoted as saying that the camps contained no "terrorists". Worse still, the Phalangists that were sent into the camps numbered only 150 - if they were supposed to confront 2.000 soldiers, that seems a bit optimistic in the capabilities of the militia. In all likelihood, the camps contained no PLO fighters.
c) The second point of major criticism was the ability of the IDF command posts to see what happened in the camps. The Israeli forward command post was a five story building a mere 200m away from Shatila. According to the report, the IDF command couldn't have seen what happened in the camps, not even with binoculars. A ludicrous claim, as independent tests shortly after the massacre proved this wrong - even without binoculars. And even if they couldn't see everything in the camps, there was a mass grave just 300m from the command posts that would have been very, very hard to miss.
d) The report concluded that the IDF had no way of knowing that the massacres were ongoing. They reached this conclusion despite recognizing that the militia shared the IDF command post, where several Israeli’s overheard and reported such communications as militia members radioing Hobeika with questions about what to do with 50 women and children and later with 45 prisoners – the responses being ‘This is the last time you're going to ask me a question like that, you know exactly what to do.’ and ‘Do the will of God.’ respectively. Another message reported 300 casualties at that point. All these events were reported by members of the Israeli staff to their superiors, but were not acted upon. Even on the 17th of September, Israeli reporter Ze'ev Schiff got an anonymous tip from inside the military staff that a massacre was occurring. All these things are accepted as fact in the report. Nonetheless, the commission concluded that the IDF didn’t know the massacre was happening.
e) There were accusations that Israel even supplied material aid in the massacres, in the form of supplying bulldozers and illuminating the camp with flares at night. Supposedly, Hobeika’s militia was flown into Beirut by the Israeli military as well.
f) Another point of criticism revolves around the question if Israel knew of the possibility of a massacre before it even took place. This knowledge would imply criminal negligence or would even imply complicity. The commission mentions this possibility, but rejects it without giving any reasoning. The criticism here is summed up by the words of author Izhar Smilanski: ‘We let the hungry lions loose in the arena and they devoured people. So the lions must be the guilty ones, mustn’t they? They did the killing, after all. Who would have dreamed, when we opened the door for the lions and let them into the arena, that they’d gobble people up like that’ There were in fact many reports of concerns and predictions shortly after Bashir’s death about the nigh-on certainty of revenge and massacres, including by Mossad leaders, the Chief of Staff and the Deputy Prime Minister.
g) In addition to the last point, Hobeika’s militia was known for its brutality and for the massacres it committed, even before Sabra and Shatila. There were plenty of other militias who could’ve been sent in, but the Phalangists were chosen. The implication is clear.
h) The punishments suggested by the commission were often ignored. Sharon lost his minister of defense post, but stayed on as minister. He was even allowed to chair in several defense commissions, leaving him in de facto control of the defense post. Eitan wasn’t punished because he was on the verge of retirement. Yaron wasn’t supposed to have gotten a command for three years, but was appointed as chief of manpower and training shortly after the publication of the report.
These were just a few of the criticism on the report. Since then, there have been a few other commissions – most notably the MacBride commission – but these haven’t been accepted by Israel. Any criticism has been sharply countered, with browbeating, lawsuits and disinformation.
But let me be totally clear: Israel holds a direct responsibility for what happened in Sabra and Shatila and there are some very damning pieces of evidence that imply that members of the Israeli government and IDF were well aware of what was going to happen beforehand, most notably Ariel Sharon.
If there are any questions or if you want to know more about anything, just ask. I left out a lot because this is long enough as it is. As for sources, should I just upload my Bachelor's thesis? It's not in English, though.
e: How the hell do you leave space between paragraphs on this site? Goddamn.