A serial killer met his third victim while on unescorted leave from a secure mental hospital where he had been locked up for strangling his last girlfriend, a court heard. Violent and “controlling” Theodore Johnson, 64, attacked mother-of-four and grandmother Angela Best, 51, beating her over the head with a claw hammer and throttling her with a dressing gown belt after she left him for another man. He then jumped in front of an express train at Cheshunt station in Hertfordshire.As he was being treated for severe injuries, police went to his flat and found Ms Best dead in the living room.Johnson pleaded guilty at the Old Bailey to murdering Ms Best and yesterday was jailed for life with a minimum term of 26 years.In 1981, he was convicted of killing his wife by pushing her off a balcony and then, in 1993, a couple of years before meeting Ms Best, he was convicted of strangling another girlfriend in London. Afterwards, Ms Best’s sister Lorraine Jones accused Johnson of attempting to “play the system” to get away with murder.She said: “This convicted murderer tried to play the system as he has successfully done before.”He used diminished responsibility as the cause for his murderous actions.”This time, however, he has eventually pleaded guilty to murder after 12 months since his arrest and subjecting our family to unnecessary additional trauma. Lorraine Jones accused Johnson of attempting to “play the system” Credit: Yui Mok/PA The Jamaican, who suffered from a personality disorder and depression, was on unescorted leave when he met Ms Best as he was taking a City and Guilds course on furniture restoration on two days a week.In October 1997, about a year after their relationship began, Johnson successfully applied to a tribunal for a conditional discharge.One of the conditions was that he alerted authorities to any relationship with a woman, which he failed to do for years.He kept his relationship a secret from doctors and social workers who continued to monitor him in the community.He was last seen by a social worker and psychiatrist on December 8 2016 – days before the murder – and was not found to be depressed and continued to deny being in a relationship.Ms Best only found out he had killed a previous partner when she found letters and confronted him, the court heard. The court heard that Ms Best, of Tottenham, north London, had been in a relationship with Johnson since around 1996, after moving to the capital from Manchester.At the time, Johnson was still the subject of a hospital order, having been refused conditional discharge around that time. Angela Best was murdered by JohnsonCredit:PA “He has shown in all cases he was clearly of sound mind. He knew what he was doing when he planned and executed the horrific murder of our beloved Angela.” Camden and Islington NHS Trust, which was responsible for Johnson’s care in the community since 2004, said it would provide Ms Best’s family with an independent report and that Johnson’s treatment complied with conditions set by the Mental Health Tribunal which oversaw his discharge in 1997. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.