Saeed al-Qashash was born in 1979 in Jordan. At the age of 19, he was a student facing significant academic pressure from his family regarding his performance in secondary school exams. This familial pressure reportedly contributed to his mental and emotional distress. There is limited public information about his early life beyond these details.

On June 10, 1998, in the outskirts of Amman, Jordan, Saeed al-Qashash committed a mass murder, killing 12 individuals. The victims included his parents, Thuria and Amin; his two brothers, Mohammed and Mostafa; his four sisters, Karimeh, Wafa, Mervit, and Insaf; his brother-in-law; his two nephews, aged two and three; and his 19-year-old classmate, Atta Shalan. Al-Qashash lured each victim individually to the basement of his family home, where he shot them in the back of the head with a 7mm pistol. After the killings, he piled the bodies, covered them with blankets and carpets, and sealed the basement with bricks and cement before fleeing the scene.

He was apprehended by authorities on June 12, 1998, and confessed to the murders. During his trial, al-Qashash pleaded for leniency, but the court convicted him on 12 counts of premeditated murder and sentenced him to death on November 30, 1998. He was executed by hanging at Swaqa Prison, approximately 60 miles south of Amman, on June 6, 1999.