Chun was a graduate of the Korean Military Academy in 1955. He was a member of Hanahoi, a powerful group of military officials that supported his actions. He was in charge of the investigation into the assassination of President Park Chung-hee. On 12 December 1979, in what became known as the Incident of December 12th, Chun ordered the arrest of Army Chief of Staff General Chung Sung Hwa (정승화, 鄭昇和) without authorization from then-President Choi Kyu-ha. He ordered the arrest as part of the investigation of his part in the assassination. Chung Sung Hwa resisted the arrest. This led to a bloody gun fight at the Army Headquarters and the Ministry of Defense. By the next morning, Chun and his fellow military academy graduates Roh Tae-woo and Jeong Ho-yong were in charge of the Korean military.