The arrest of human rights activist Fethi Tarbel, who had been working to free Libya's political prisoners, triggered a riot in Benghazi on February 15 and ensuing protests known as the "Day of Rage." Libyan leader Colonel Muammar Qaddafi vowed to clamp down on the protests, igniting a bloody civil war that lasted for months. The UN Security Council imposed a no-fly zone on the country in an effort to protect civilians from Qaddafi's army. Troops loyal to the rebel National Transitional Council (NTC) entered the capital, Tripoli, on August 21. Qaddafi fled to his hometown of Sirte, where he was captured and killed by NTC forces on October 20.