Yes, the UN General Assembly’s approval of “non-member observer state” status for Palestine is big news. No, it does not mean that Israeli leaders should be keeping an eye out for ICC investigators.
Palestine’s new status as a sorta-kinda-maybe-state does mean that it can now join the ICC. But, as Mark Goldberg points out, if Palestine tries again to refer the situation to the court, it will be up to Chief Prosecutor Fatou Bensouda first to decide whether to open an investigation, and then whether to issue charges. At either stage, she might decide that the evidence doesn’t support proceeding, or that pursuing a case is not “in the interests of justice” (Rome Statute, Art. 53). That last one gives her broad discretion to decline to proceed, which could be useful cover if, say, she felt that it was not a real swell idea for a young institution in a politically precarious position to piss off the superpower by going after one of its most important allies. You know, hypothetically.
Additionally, the Prosecutor might conclude that she is blocked by Israeli court proceedings covering actions in Palestine (Rome Statute, Art. 19). The ICC’s jurisdiction is complementary, which means it is only empowered to hear cases that the relevant state judicial system(s) are “unwilling or unable” to prosecute. Unlike many of the states who make up the ICC’s current caseload, Israel has a competent and active judiciary that has heard numerous cases arising out of policy towards the Occupied Territories. Determining that past judicial precedent suggests an “unwillingness” to prosecute would require a complicated and messy analysis that ICC is ill-equipped to undertake.
Finally, even if the Prosecutor were willing to proceed, it is not clear what events would be eligible. The ICC’s potential temporal jurisdiction over a state’s territory starts from the day the Rome Statute entered into force for that state. For many states, that’s the day of the court’s birth, July 1, 2002, but for those states that signed the treaty after the court started its work, it’s later.
So if Palestine joined the ICC tomorrow, a straightforward interpretation of the court’s jurisdictional provisions would say that the ICC could only prosecute crimes that take place starting from December 2012. There’s a possible Hail Mary argument invoking the Eichmann precedent that new states have retroactive jurisdiction over crimes against their citizens, but there’s no reason to think that this could be passed on to the ICC. The court only inherits its members’ jurisdiction over crimes committed by their citizens, or on their territory, not crimes committed against their citizens. And extending the ICC’s jurisdiction over Palestine back in time would effectively strip Israel of jurisdiction over a portion of its territory during a time in which it was the uncontested (with regard to formal institutions) sovereign. Additionally, the fact that Palestine’s “stateness” is likely to remain a bit of an open question makes any kind of retroactivity more of a stretch.
[Late-breaking news: Kevin Jon Heller has a new post up at Opinio Juris expounding a very different view. He cites Côte D'Ivoire's April 18, 2003 acceptance of the ICC's jurisdiction back to July 1, 2002 as evidence that states can give the court retroactive jurisdiction. I don't agree that this is relevant precedent; Côte D'Ivoire was the territorial sovereign throughout the entire period, so its retroactive acceptance of jurisdiction raises none of the issues posed by a new state.]