In 1951 Straffen was s arrested for the murder of nine-year-old Cicely Batstone in Somerset. He confessed to the crime and to the murder of Brenda Goddard, aged six. Straffen was sent for trial at Somerset assizes in Taunton in October 1951 but was found unfit to plead. He was declared insane and was sent to Broadmoor asylum. In April 1952 Straffen escaped briefly from Broadmoor. When recaptured he is said to have told the police"I did not kill the little girl on the bike". Linda Bowyer’s body was found near Broadmoor and he was charged with her murder.
Unlike his previous trial Straffen was declared fit to stand trial on the basis that he understood four of the Ten Commandments. Straffen pleaded not but was convicted of her murder and sentenced to death. The then home secretary Sir David Maxwell-Fyfe commuted the sentence (subsequently released medical records made it clear that Straffen was reprieved on the grounds of insanity).
Straffen served his sentence in maximum security prisons rather than a high security hospital such as Broadmoor. He died in Frankland prison in Co Durham.