In 1937, Allen was a 25-year-old assistant chef working at the Lamb Hotel in Burford, Oxfordshire. He had been befriended by the Woodward family and often used to take their 17-month-old daughter, Kathleen Diana Lucy, for a walk.

He took her for such a walk on 21st October but he strangled the child with a clothes line and dumped the body at the side of a road. He was arrested a couple of days later when he surrendered to police.

On 6th November 1937 he was found guilty but insane and was sent to Broadmoor. Ten years later he escaped from Broadmoor dressed as a cleric. He stayed at large for two years and was dubbed by the press as 'The Mad Parson.' After his recpture he was returned to Braodmoor. He was released on 18th September 1951.