Fatah was organized as a Palestinian nationalist group in 1954, and exists today as a political party in Palestine. In 1967 it joined the Palestine Liberation Organization (PLO), an umbrella organization for secular Palestinian nationalist groups formed in 1964. The PLO began its own armed operations in 1965. The PLO's membership comprises separate and possibly contending paramilitary and political factions, the largest of which include Fatah, the Popular Front for the Liberation of Palestine (PFLP), and the Democratic Front for the Liberation of Palestine (DFLP). Factions of the PLO have advocated or carried out acts of terrorism. Abu Iyad organized the Fatah splinter group Black September in 1970; the group is arguably best known for seizing eleven Israeli athletes as hostages at the September 1972 Summer Olympics in Munich. All the athletes and five Black September operatives died during a gun battle with the West German police in what later became known as the Munich massacre. The PFLP, founded in 1967 by George Habash, on September 6, 1970 hijacked three international passenger planes, landing two of them in Jordan and blowing up the third. Fatah leader and PLO chairman Yasser Arafat publicly renounced terrorism in December 1988 on behalf of the PLO, but Israel has stated that it has proof that Arafat continued to sponsor terrorism until his death in 2004.