[1] An artist before the war Warren was employed as a commercial designer producing poster ads with the Grenada organisation.
As a result of this and the harsh treatment meted out by the Japanese guards such as the beatings and executions of escaped prisoners, the men's health and morale began to suffer in the long run.
[4] During one of the work parties, Warren was sent to build a road and stairs leading to a memorial to the Japanese dead on Bukit Batok Hill (marked with a Bukit Batok Memorial plaque today, only the stairs and road called Lorong Sesuai are still there to be seen).
[5] The chaplain of the regiment, well aware of Warren's religious conviction and artistic background, requested him to decorate the asbestos walls at the altar area of a small open attap-roofed chapel at Bukit Batok.
With charcoal salvaged from around the camp, he drew two murals: Nativity, which featured a Malay Madonna and Descent from the Cross in which he included soldiers in uniforms, using his comrades as models.
On 23 May 1942, Warren was lying comatose and was sent to Roberts Barracks in Changi which was converted for use as a hospital for POWs to recuperate.
So they asked him if he would do some paintings for St Luke's Chapel, which was recently converted from the ground floor of Block 151, near the area where Warren was recuperating.
[6] On 30 August 1942, at the time when Warren was preparing the draft drawings of the murals, the Japanese began an action which would become known as the Selarang Barracks incident.
It was an incident concerning seventeen thousand Anglo-Australian POWs, who were forced to vacate their buildings and be exposed for nearly five days in the open without water or sanitation for refusing to sign a "No Escape Pledge".
The lower portion of St Luke in Prison mural was almost completely destroyed when it was demolished to make a link to an adjoining room.
Warren was later sent to Kranji in the north of Singapore, not far from the Causeway to Malaya, and remained there until the Japanese surrender on 15 August 1945.