A mysterious man who died by suicide in an Idaho church in 1982 has finally been identified - and investigators have suggested he is likely the infamous Tylenol Murderer, who killed seven with cyanide-laced painkillers.

The man - who was nicknamed 'the Unknown Wanderer' after his death - was Doctor Mathew Francis Betkouski, Ada County Sheriff's Office said in a press conference in Boise on Wednesday.

Betkouski, of California, was found dead beneath a pew at Sacred Heart Catholic Church in the Idaho city on December 4, 1982, following a confessional service, Sheriff Matt Clifford said.

He died of cyanide poisoning - the same method used to kill the seven victims of the Tylenol murderers just three months previously, during the final week of September 1982.

Betkouski was finally tracked down thanks to one of 30 keys found on his body after his death, which was featured in a famous 1990 episode of Unsolved Mysteries. He was not linked to the Tylenol homicides at the time.

That key had an etching that led to an address in Jacksonville, Florida. A property records search revealed Betkouski was registered as living there until 1989.

But when investigators tracked down one of his relatives, they confirmed he had been missing since 1982 and had been declared dead in absentia in 1989. That explained why he still appeared on the property record for years after his death.

A DNA sample taken from that man was so close to material taken from Betkouski that forensic scientists were able to declare the two men brothers.

ACSO Cold Case Detective Tim Cooper also produced multiple pieces of evidence that link Betkouski to the Tylenol Murders, although he said his office lacked a 'smoking gun' piece of evidence that would allow them to definitively name Betkouski as a suspect.

While working as a chemist at the secretive White Sands testing facility in New Mexico, Betkouski is said to have said that tainting capsules with poison would be the perfect way to murder someone.

He was fired over a disturbance at a local pharmacy and was someone who had a 'documented fascination' with chemistry and explosives, Cooper said.

A woman was killed by cyanide poisoning at the same lab while he worked there and her death remains unsolved.

Years after his death, authorities tracked down his family and visited his childhood home, where they uncovered a small bottle of cyanide that was 'likely homemade' and a map of Chicago, Cooper said.

The cyanide was of a different variety from the type used in the Tylenol murders in the Windy City.

He also made several phone calls to pharmaceutical and chemical supply companies in Pennsylvania just weeks before the Tylenol homicides.

Cooper said that police also recovered photos of Betkouski visiting Chicago, and that they were likely taken around December 1981.

Detective Cooper also highlighted rumors about Betkouski making a possible confession in the Catholic Church shortly before his suicide.

He did not share those rumors and said they had never been verified, amid online chatter that Betkouski may have confessed to the Tylenol Murders shortly before taking his own life.

Along with the filled keychain, a typed suicide note and $1,900 were found on Betkouski at the time of his death, according to Clifford.

In the note, he said that he wanted the money to be used for his funeral and cremation. It was signed 'Wm. L. Toomey.'

He was never reported as a missing person, but the sole key help police traced him to Jacksonville, Florida, and eventually to a living relative in Los Angeles who confirmed Betkouski's identity.

Cooper said that Betkouski often talked about cyanide, referring to it as 'a less messy way of taking a person's life.'

The infamous Tylenol murders claimed the lives of seven people across the Chicago area after they ingested extra-strength Tylenol capsules that were laced with cyanide.

The youngest victim, Mary Kellerman, 12, was the first person to die.

Just hours later, Adam Janus, 27, died, and while his family was grieving at his home, two more of his relatives, Stanley Janus, 25, and Theresa Janus, 19, passed away after taking pills from the same bottle.

Mary McFarland, 31, Paula Price, 35, and Mary Reiner, 27, also died after taking the tainted pills.

Their deaths triggered a nationwide Tylenol recall and sparked the invention of mandatory tamper-evident safety seals in consumer goods and pharmaceutical industries.

The murders remain unsolved nearly 44 years later.

Over that time, investigators identified some suspects, but only one man, James Lewis, was convicted.

Lewis wrote a letter around the time of the deadly poisonings to Johnson & Johnson - the former makers of Tylenol - stating that the deaths would stop if the company wired $10 million to a Chicago bank account.

He admitted to writing the letter, but claimed it was only to embarrass a travel company that the bank account was tied to.

In the end, he was convicted of extortion in connection with the letter and sentenced to 10 years in prison.

He was released in October 1995 and died at his home in Cambridge, Massachusetts, in July 2023.

Another man, Roger Arnold, was also investigated by police after he confessed to possessing potassium cyanide - the same substance used in the 1982 murders.

A bar owner, Marty Sinclair, also reported hearing the dock worker discussing killing people with white powder.

He was held several times by police, but never charged.

Arnold did, however, serve time for shooting a man whom he thought was Sinclair, in the summer of 1983.

He was convicted in January 1984 and served 15 years of his 30-year sentence. Arnold died in June 2008.

After his body was exhumed, it was used for DNA testing in the Tylenol case and did not match any of the DNA found on the bottles.