John Straffen became the UK's longest serving prisoner after he murdered three little girls in the 1950s.

“John Straffen will always be remembered as one of the country's most notorious child murderers”
Straffen’s Obituary, The Guardian, 22 November 2007
John Thomas Straffen is born in Borden, Hampshire on 27 February 1930, but as his father is in the armed forces Straffen spends his early years in India. The family return to England in 1938, and decide to settle in Bath.
Although at school Straffen is described as being quite affectionate and not aggressive towards other children, it is noted that he is a bit of a loner and resents authority. He is in virtually constant trouble from the age of eight, committing minor thefts and truanting from school. At age 10, his IQ is just 58, way below the average of 100. As a result he is sent to various residential schools called “colonies” which educate juvenile delinquents and children with what we would now call learning difficulties. Straffen is released back into the general population aged 16.
A year later Straffen is certified as “feeble-minded” by authorities after he kills five chickens. He is sent to another colony which is located in Almondsbury, north of Bristol.
After four years in Almondsbury, Straffen is released on licence. An electro-encephalograph examination carried out by a Bristol hospital reveals that he has "wide and severe damage to the cerebral cortex”. This is the outer area of neural tissue which covers the cerebrum and cerebellum of the brain. It is likely that an attack of encephalitis in India as a child caused this damage.
Just days after this diagnosis he would kill for the first time. At his trial, medical witnesses will testify that it is this brain injury that has impaired Straffen’s moral understanding, which contributed to his crimes.