It's still impossible to say for sure whether the Chilean poet and politician Pablo Neruda was poisoned, resulting in his death in 1973. That's according to forensics experts involved in a report that outlines the findings of an investigation into the Nobel Laureate's demise.

This comes after outlets across the world reported statements from Neruda's nephew, Rodolfo Reyes, who had told journalists that the highly anticipated report — which was released to lawyers in Chile on February 15 but remains unavailable to the public — proved the poet was poisoned.

The forensics experts did not confirm Reyes' statements when they were initially published but told DW a day later, on February 16, that they were untrue.

"We note that there's something interesting, and more work should be done, but in no way can we conclude [Neruda] was poisoned," geneticist Hendrik Poinar told DW in an email.

"So, we can't close the case (no smoking gun) but we can't — yet — rule it out either," wrote Poinar, adding that this was the consensus among all the researchers involved in the report.

Their report is the culmination of years of research conducted on the poet's remains.

Neruda was a long-time member of Chile's Communist Party and an adviser to President Salvador Allende. His death came just weeks after Allende was overthrown in a coup by Augusto Pinochet, whose military regime would murder and jail thousands of political opponents.

Years of research into Neruda's death

In 1977, four years after Neruda's death, doctors reported that he had suffered from prostate cancer.

But, almost four decades later, Neruda's driver revealed that the poet had told him, when Neruda was on his death bed, that he had been stabbed in the stomach. 

That revelation prompted a renewed interest in Neruda's death and the subsequent investigation .

In 2017, researchers said they had found that Neruda had not died from prostate cancer, as originally reported by doctors, and that prompted them to try and figure out the true cause of the death.

The scientists found clostridium botulinum, a toxic bacterium, in one of Neruda's exhumed molars.

This seemed like a significant finding because in 1981 political prisoners in Chile were known to have been poisoned with that very bacteria.

Clostridium botulinum (also known as C. botulinum) produces lethal botulinum toxins, which can block nerve functions and lead to respiratory and muscular paralysis.

Proof of bacteria, but no proof of poisoning

Since the discovery of C. botulinum in Neruda's tooth, a team of Chilean, Danish and Canadian researchers have studied the poet's remains.

First, they wanted to see whether the bacteria could be detected elsewhere in the poet's body.

They found some C. botulinum in Neruda's bones, but they have yet to discern whether it's from the same source as that found in the tooth, said Poinar. 

Second, they wanted to know whether the bacteria had been present in Neruda's body at the time of his death. That would enable them to rule out the possibility that the C. botulinum had entered his body afterward — transferred from the material of the coffin, for example.

The researchers investigated the DNA of the bacteria and compared it to other bacteria found in Neruda's remains. They found that the DNA of the C. botulinum from Neruda's tooth was damaged in a similar way to other DNA samples taken from Neruda's oral bacteria. That suggests, the researchers say, that the C. botulinum could have been present when the poet died.

An independent expert on botulism, John Austin, said the researchers' conclusion seemed plausible, assuming that their DNA sequencing was correct. Austin leads the Botulism Reference Service for Canada and conducts research on botulinum toxin-producing strains of clostridium.

But both Austin and the scientists who conducted the research on Neruda's remains told DW this doesn't explain how C. botulinum came to be in the poet's tooth, and it doesn't confirm he died of botulism.

Austin added that the mere presence of C. botulinum is not harmful to humans — what's harmful is the toxins that it produces when it grows.

He said when a person dies, bacteria multiply in the body to start the decomposition process. It's possible there was a small number of harmless C. botulinum spores in Neruda's mouth when he died that eventually grew after death.

The researchers said one way to conclusively prove the poet had been poisoned would be to compare the C. botulinum strains found on Neruda's tooth with the C. botulinum strains found in the remains of the 1981 political prisoners.

But "we don’t even know if those remains exist," Poinar told DW. "If they do... we would want to conduct those experiments."

Death still a mystery

A lot is still unclear. For example, Austin said if Neruda did indeed die from the C. botulinum found in his molar, his driver's stabbing claim doesn't add up.

"If someone were killed by injection of botulinum toxin, this would not result in the presence of C. botulinum DNA in a tooth," he told DW.

Fabrizio Anniballi, another botulism expert who was not directly involved in the research on Neruda's remains, said "based on the publicly available information, it is unlikely that Pablo Neruda died of botulism." Anniballi runs Italy's National Reference Center for Botulism.

"I read that he was given an injection into the belly and that, after six hours, he died," Anniballi told DW. "Six hours is generally too short to trigger botulism and cause the subject's death. To better assess the plausibility of botulism, it would be desirable to know his symptoms before the end."

Poinar said it was hard to get exact information on the poet's condition at the time of his death. 

"Others working on the case in Chile may have a better handle on this, but my sense is that it was a very difficult situation with few people attending to those in the hospital," said Poinar.

Spores of bacteria do not confirm poisoning

Meanwhile, Anniballi questioned how it was possible that the researchers found C. botulinum in DNA form.

He said botulism poisoning was not caused by C. botulinum but by its neurotoxins. And because neurotoxins are proteins, they degrade if they come into contact with enzymes called a protease.

The stomach and intestines contain many such proteases, said Anniballi, and that makes it very unlikely that researchers would find these neurotoxins in a 40-year-old corpse.

Anniballi said when a person gets botulism poisoning, they consume both the neurotoxins and the C. botulinum.

The bacteria is a spore-forming microorganism found in any environment that can contaminate foods — such as soils, sediments, dust and water.

If food containing the C. botulinum bacteria is not properly preserved, the spores can grow and replicate. And unlike the aforementioned neurotoxins, which can degrade, the spores "are highly resistant to environmental conditions and can be found after hundreds or thousands of years," said Anniballi.

Anniballi said it is therefore likely that the researchers working on Neruda's remains had recovered damaged DNA from these spores. But he said the spores still don't necessarily indicate that Neruda was poisoned. They just indicate that he may have died with some of the bacteria in his mouth.

Edited by: Zulfikar Abbany