After being released in 1971, Young got a job in a factory in Bovingdon, Hertfordshire, where he began poisoning his colleagues, resulting in two fatalities and several critical illnesses.

[1] The Young case made headlines in the United Kingdom and led to a public debate over the release of mentally ill offenders.

First his stepmother Molly suffered vomiting, diarrhoea and excruciating stomach pain, which she initially dismissed as bilious attacks.

While on the train to work an hour later, she began to hallucinate, had to be helped out of the station and was eventually taken to hospital, where doctors came to the conclusion that she had somehow been exposed to the poisonous Atropa belladonna.

Psychiatrist Dr Christopher Fysh testified that Young had a psychopathic disorder rather than a mental illness and had failed "to develop a normal moral sense."

"[4] Fysh recommended that Young be detained at Broadmoor Hospital in Berkshire, an institution for patients with mental disorders who have committed criminal offences.

Young pleaded guilty to three charges of poisoning his father, sister and school friend and was convicted of "malicious administration of a noxious thing to inflict grievous bodily harm".

[4] The judge, Justice Melford Stevenson, ruled that Young was to be detained under Section 60 of the Mental Health Act at Broadmoor.

He also continued his interest in Nazism, reading William Shirer's The Rise and Fall of the Third Reich and Lord Russell's The Scourge of the Swastika.

[9] Five years later, in June 1970, Broadmoor psychiatrist Edgar Udwin wrote to the Home Secretary to recommend Young's release, announcing that he was "no longer obsessed with poisons, violence and mischief.

Young duly returned with the required authorization on Bedford College headed notepaper and was sold 25 g of antimony potassium tartrate.

[12] On the night of February 10, Sparkes fell violently ill, exhibiting diarrhoea, pins and needles in his legs and pains in his testicles; earlier in the evening he had accepted a glass of water from Young.

[12] Young secured a job as assistant storekeeper at John Hadland Laboratories in Bovingdon, Hertfordshire, near his sister's home in Hemel Hempstead.

On his application, Young falsely claimed that his lack of employment history was because he had suffered a nervous breakdown following the death of his mother in a car accident.

During breaks he usually sat alone reading, invariably a book on one of his favourite subjects: war, chemistry, the Nazis or famous murderers.

His health improved after a week-long holiday, but on his return Young put a lethal dose of thallium in his afternoon tea.

[18] Foster recalled Young remarking how sad it was that "Bob should come through the terrors of Dunkirk only to fall victim to some strange virus.

Tilson found the tea too sweet for his liking (Young had added sugar to disguise any unusual taste from the thallium) and therefore did not drink it all.

"[25] Fred Biggs, a 56-year-old local councillor and part-time employee at Hadland, was poisoned by Young with antimony, prompting the typical "Bovingdon Bug" symptoms.

[26] The firm's medical officer, Dr Iain Anderson, told staff that he had ruled out heavy metal poisoning as a possible cause, which led to an argument with Young, who insisted that the symptoms displayed by victims pointed to this diagnosis.

He quickly discovered that Young had a deep knowledge of poisons and toxicology, which prompted John Hadland, the firm's owner, to contact the police.

When police searched his bedsit, they discovered a large stash of bottles containing poisons, including 434 milligrams of thallium and 32.33 grams of antimony, the latter 200 times a lethal dose.

[29] Upon further questioning by police, Young admitted that the initials in the diary referred to his co-workers ('F' was Fred Biggs, 'D' was David Tilson and so on).

[31] He pleaded not guilty, which made it difficult to find a barrister willing to represent him; the trial date had to be postponed several times.

[33][34] Examination of Biggs' internal organs found thallium in his intestines, kidneys, muscles, bones and brain tissue.

Brady wrote that Young "was genuinely asexual, finding even discussion of sexual matters not only uninteresting but also distinctly distasteful... Power and death were his aphrodisiacs and raisons d’être.

[39] On 29 June 1972, the day Young's trial ended, Home Secretary Reginald Maudling gave a statement in the House of Commons about the issues raised by the case.

[42] Maudling also announced an inquiry to review the management of mentally ill offenders in the criminal justice system, to be chaired by Lord Butler.

For the previous eighteen months he had suffered from severe chest pains, which he traced back to an encounter, in a Hemel Hempstead pub, with a young man obsessed with poisons and chemicals.

In 2021, Carol Ann Lee released a true crime book titled A Passion for Poison: Serial Killer.