Every state has an obligation under international law to seek out and to prosecute terrorists. It is codified directly in many different sources, and is also deducible from the binding Nuremberg Principles.
Terrorism is an established crime under international law.
I do not believe the law of nations imposes the same responsibility or liability on nonstate actors, such as the PLO, as it does on states and persons acting under color of state law. The PLO, as well as the Palestine Information Office, the National Association of Arab Americans, and the Palestine Congress of North America, were named defendants in this suit for compensatory and punitive damages. The PLO terrorists landed by boat in Israel and set out on a barbaric rampage along the main highway between Haifa and Tel-Aviv. They seized a civilian bus, a taxi, a passenger car, and later a second civilian bus. They took the passengers hostage.