[masraum]

Originally Posted by GH85Carrera

Stray Dogs Dug at Same Bench Daily, Janitor Checked Beneath and Called FBI!
Janitor Andrew Trevor maintained the city park for decades, but the stray dogs' aggression near the old oak bench puzzled him.
The pack returned daily, clawing at the dirt until their paws bled, ignoring any food he threw.
Suspecting a buried animal, Andrew decided to clear the area before the weekend.
He grabbed his shovel and pickaxe from the shed at sunset.
The soil was incredibly compacted, requiring hours of intense labor.
Three feet down, his shovel struck a hard, metallic surface.
Clearing the debris, Andrew exposed a heavy, wax-sealed metal container wrapped in decaying plastic.
He pried the rusted latch open, but the moment the lid creaked back and revealed the items inside, Andrew froze and immediately dialed the FBI!
Inside the container, agents secured fifty-one vintage glass vials containing thallium, a lethal heavy metal poison.
Forensics linked the cache to a notorious serial poisoner from the 1970s who had died in prison without revealing his stash.
Investigators determined the poison had been buried decades earlier, when the land was still an undeveloped wooded lot long before the park and bench were constructed.
The stray dogs had been frantically digging because the killer had used a beef-tallow mixture to seal the corks, the scent of which had finally seeped through the ground after all these years.
Andrew’s discovery solved a decades-old cold case and removed a deadly hazard from the public park.

I suspect that's a completely fictitious story.
Although it could be referencing this guy who used thallium and antimony.
https://en.wikipedia.org/wiki/Graham_Young

Graham Frederick Young (7 September 1947 – 1 August 1990), also known as the Teacup Poisoner, was an English serial killer who murdered his victims with poison.

Obsessed with poisons from an early age, Young poisoned the food and drink of relatives and school friends. He was caught when his teacher became suspicious and contacted police. Young pleaded guilty to three non-fatal poisonings and, at age 14, was detained at Broadmoor Hospital. He later took responsibility for the death of his stepmother, though this has not been proven.

After being released in 1971, Young found a job in a factory in Bovingdon, Hertfordshire, where he poisoned some of his colleagues, resulting in two deaths and several critical illnesses. He was convicted on two counts of murder and two counts of attempted murder in 1972. Young served most of his life sentence at Parkhurst Prison, where he died of a heart attack in 1990.[1]

Young's case made headlines in the United Kingdom and led to a public debate over the release of mentally ill offenders. Within hours of his conviction, the British government announced two inquiries into the issues his trial had raised. The Butler Committee led to widespread reforms in mental health services, while the passage of the Poisons Act 1972 put severe restrictions on the purchase of deadly poisons. Young's life story inspired the film The Young Poisoner's Handbook (1995).

I found a link that indicated that this guys confession led prosecutors to his caches of thallium and antimony.