The Marines pulled out on 10 September, a week or more before their mandate expired; the Italians left on 11 September and the French on 12–13 September (Ménargues, Hanf). Their last landing craft bore a 'Mission accomplished' banner. The Sabra and Chatila massacre began a few days after the last French troops left.

Bashir Gemayel was killed at about 4 p.m. during his weekly visit to the Kataeb office in Ashrafieh, nine days before taking office. The bomb, about 35 kilos of explosive, had been placed two days earlier in the flat above by Habib Tanios Chartouni, a member of the Syrian Social Nationalist Party, arrested on 16 September (Ménargues). Prime Minister Wazzan announced the death at midnight. Hanf counts 26 dead.

In Ménargues's account of the Bikfaya funeral, Bashir's coffin was carried from the church of Mar Abda onto a gun carriage before the entire government, the diplomatic corps and every deputy, even those who had boycotted his election. Israeli troops had entered West Beirut at 5 a.m. that day, breaching the agreement negotiated by Philip Habib.

Israeli troops entered West Beirut at 5 a.m. on 15 September, the morning after Bashir Gemayel's death, against the commitments given through Philip Habib; Lebanese leftist militias fought them in parts of the city.

Jawad Boulos was one of three 'wise men' in the leadership of the Christian Lebanese Front, with Fouad Ephrem Boustani and Charles Malek (Hanf).

The massacre lasted from the evening of Thursday 16 September to the morning of Saturday 18 September (Traboulsi gives 15-17, Hanf 17-18). The killers were militiamen of the Lebanese Forces' security service under Elie Hobeika, together with men of Saad Haddad's South Lebanon militia. The Israeli army, which controlled the area after entering West Beirut on 15 September, let them into the camps, lit the camps with flares at night and watched from command posts nearby. Israel's Kahan Commission, published on 7 February 1983, held the Phalangists directly responsible and found Defence Minister Ariel Sharon personally responsible, recommending his removal; it also attributed indirect responsibility to other Israeli political and military leaders. Estimates of the dead range from about 460-800 to 3,500; Bayan Nuwayhed al-Hout's survey found victims of twelve nationalities, about half Palestinian and more than a quarter Lebanese.

Amine Gemayel was elected in the same Fayadiyeh barracks as his brother, with 77 votes of the 80 deputies present (Hanf). On the evening of 20 September Israeli ministers Yitzhak Shamir and Ariel Sharon had met him secretly at Dbayeh (Ménargues).

The attempt on Walid Jumblatt left him only slightly hurt. Hanf sees it as one more spur to Druze mobilisation, which put about 30,000 men under arms.

Fisk and de Clerck and Malsagne count 63 dead, 17 of them Americans, and Fisk about a hundred wounded. Many victims were Lebanese queuing in the visa section. The bomb struck a meeting of the CIA's senior regional officers. De Clerck and Malsagne describe the vehicle as a van, Fisk as a truck.

Ménargues dates the handover to 28 April 1983. Held in an army intelligence cell at the Defence Ministry in Yarze, Chartouni admitted the killing before the military prosecutor that day. The case was later handed by Amine Gemayel's cabinet to a constitutional High Court that had never been created; he was freed on 13 October 1990.

Massacres were committed on both sides: Druze fighters killed Christians at Bmaryam, Bhamdoun, Ma'asir al-Chouf and many other villages, and Lebanese Forces fighters killed Druze at Kfarmatta and in villages on their line of retreat. For September to December 1983 de Clerck and Malsagne give more than 1,500 Christians and 207 Druze massacred, 324 PSP and 368 Lebanese Forces fighters dead, and over 163,000 Christians driven from the region. Traboulsi gives 62 villages destroyed, Hanf about sixty.

The Lebanese army had under 24 hours' warning, Fisk writes, before Israeli troops began leaving Aley and the Chouf on the evening of 3 September; by the morning of the 4th they had gone. De Clerck and Malsagne count more than 10,000 Christians from over 60 villages sheltering in Deir el-Qamar.

From 19 September the destroyer John Rodgers, then the cruiser Virginia, shelled Druze positions at Souk el-Gharb. Washington cited US personnel's safety; Fisk and Hanf see entry into the civil war. Only the frigate Bowen had fired before, on 8 September, at a Druze battery hitting the Marine compound.

US aircraft struck Syrian positions on 4 December. Fisk counts one plane brought down, with the pilot dead and the co-pilot taken prisoner (Jesse Jackson obtained his release in January 1984); Hanf counts two planes lost. Hanf also places, without a date, the deaths of eight Marines from Syrian artillery fire in the same episode.

The New Jersey fired shells, not bombs: one-ton 16-inch rounds, according to Fisk. De Clerck and Malsagne say its rounds often missed, by up to 9,000 metres, and killed civilians; Christians called it 'New Jersa', a new shame.

On 15 December, after 102 days, the siege of Deir el-Qamar ended. Israel brokered the departure of Samir Geagea's Lebanese Forces and most refugees for East Beirut; the town was left mainly to its elderly.