Answer based on context:

Hoping to take the stronghold by surprise, on May 7 Pontiac entered Fort Detroit with about 300 men carrying concealed weapons. The British had learned of Pontiac's plan, however, and were armed and ready. His tactic foiled, Pontiac withdrew after a brief council and, two days later, laid siege to the fort. Pontiac and his allies killed all of the British soldiers and settlers they could find outside of the fort, including women and children. One of the soldiers was ritually cannibalized, as was the custom in some Great Lakes Native cultures. The violence was directed at the British; French colonists were generally left alone. Eventually more than 900 soldiers from a half-dozen tribes joined the siege. Meanwhile, on May 28 a British supply column from Fort Niagara led by Lieutenant Abraham Cuyler was ambushed and defeated at Point Pelee. After receiving reinforcements, the British attempted to make a surprise attack on Pontiac's encampment. But Pontiac was ready and waiting, and defeated them at the Battle of Bloody Run on July 31, 1763. Nevertheless, the situation at Fort Detroit remained a stalemate, and Pontiac's influence among his followers began to wane. Groups of Native Americans began to abandon the siege, some of them making peace with the British before departing. On October 31, 1763, finally convinced that the French in Illinois would not come to his aid at Detroit, Pontiac lifted the siege and removed to the Maumee River, where he continued his efforts to rally resistance against the British.

How many days after withdrew did he siege the fort?
2