For nearly 50 years, the death of Nobel Prize-winning Chilean poet Pablo Neruda has been shrouded in mystery, with longstanding allegations that he had been assassinated. Now, new forensic evidence has emerged that the literary great may have been poisoned.

Researchers from McMaster University in Hamilton, Ont., along with colleagues from the University of Copenhagen in Denmark, presented their findings on Wednesday to a Chilean judge and said Neruda’s body had evidence of Clostridium botulinum in one of his molars.

C. botulinum is a strain of bacteria that can produce botulinum, described by researchers as “one of the deadliest toxins known to mankind.” The toxin attacks the body’s nervous system and often leads to paralysis, difficulty breathing and even death — an illness known as botulism.

In addition to the C. botulinum found in the molar, researchers also found small amounts of the bacteria at Neruda’s burial site. The C. botulinum DNA samples in both the molar and the burial site were damaged in a similar way, suggesting that the bacteria had likely been there when he died and was not due to subsequent environmental contamination.

“We’ve employed methods identical to those used to reconstruct the bacterial genome of the Black Death from 700-year-old victims,” McMaster University evolutionary geneticist Hendrik Poinar said in a news release.

Neruda, who had also been a Communist Party politician and a staunch supporter of left-wing Chilean president Salvador Allende, was hospitalized for cancer in September 1973, right around the time Gen. Augusto Pinochet seized power in a coup d’état and overthrew Allende.

Neruda died 12 days after the coup. Official records say Neruda had died from complications from prostate cancer, but the poet’s driver, Manuel Araya, argued for decades that he was poisoned.

“The notoriety of Neruda’s suspicious death and the analysis of it is symbolic of the investigation into each unsolved death that occurred during Pinochet’s dictatorship,” said McMaster researcher Debi Poinar in the news release.

A test conducted in 2013 after Neruda’s body was exhumed concluded that there was no evidence to suggest that his death was linked to anything other than natural causes, but Neruda’s family and Araya were not convinced.

Araya told The Associated Press last month he was convinced his former employer had been given “an injection in the stomach” at the hospital after hearing this version of events from a nurse.

In 2015, the Chilean government said it was “highly probable that a third party” was responsible for Neruda’s death.” Two years later, an international team of investigators concluded that the official cause of death was wrong, but did not say at the time what had killed Neruda.

“Perhaps it will be impossible to have a definitive answer as to how the poet died, but so far, the possibility of poisoning by a third party has not been ruled out by the scientific evidence we have found to date,” Debi Poinar said.

With files from The Associated Press