Under Chin's authority, the MPAJA killed those they considered to have been Japanese collaborators during the war, who were mainly Malays. This sparked racial conflict and Malay retaliation. Disciplined killer squads were also dispatched by the CPM to murder European plantation owners in Perak, and Kuomintang leaders in Johor. The Malayan government's subsequent declaration of a state of emergency on 18 June 1948 marked the start of the Malayan Emergency. Perak and Johor became the main strongholds of the communist movement. In the early stages their actions were not co-ordinated, and the security forces were able to counter them. Earlier in 1947, the head of the Perak's Criminal Investigation Department, H. J. Barnard, negotiated an arrangement with the Kuomintang-influenced OCAJA leader Leong Yew Koh. This resulted in most OCAJA members being absorbed into the national Special Constabulary, and fighting against the MPAJA's successor, the Malayan National Liberation Army (MNLA).