When Rodney Marks died on May 12, 2000, authorities had plenty of reasons to be suspicious.
Marks was only 32, in otherwise good health, and the bizarre symptoms that killed him struck out of nowhere.
But the strangest fact of all was where Marks died: at the South Pole's Amundsen-Scott research station.
Almost 20 years later, the reason behind Marks' sudden death is still unknown. But the few clues we have suggest he could be the South Pole's only unsolved murder.
A sudden death
Marks, an astrophysicist from Australia, had been working at the South Pole since 1997, and lived at the Amundsen-Scott station.
The research center, which is run by America's National Science Foundation, is one of world's loneliest workplaces.
The station is surrounded by ice, freezing wind, and left in total darkness for six months of the year.
But Marks had a good job, and was living with his fiance Sonja Wolter, who was working as a maintenance specialist to stay close to him through the coldest months of the year.
On May 11, Marks suddenly felt sick while walking from his workplace to the base. He visited the station's doctor, Robert Thompson, right away, but his condition would never improve.
Marks experienced stomach pain, nausea, and a fever for 36 hours before he finally died.
But Thompson could not identify what had killed Marks.
A cold case
The NSF announced that Marks had died from natural causes, but ordered his body to be flown out of Antarctica for more tests.
It took six months (waiting out the worst of the South Pole's weather) but his body was finally flown to New Zealand.
An autopsy revealed Marks had been poisoned by a cleaning solvent called methanol, and the working theory was Marks had drunk the chemical by accident.
But when New Zealand police tried to dig deeper, they hit a wall of silence.
Detectives say that the NSF and the Raytheon corporation, which staffed the base, did not cooperate with their investigation.
They even refused to provide detectives with a list of Marks' coworkers. Once police finally found the list, just 13 out of 49 workers assisted their investigation.
"To be frank, I think there is more there; there must be" one detective said.
"I suspect that there have been people who have thought twice about making contact with us on the basis of their future employment position."
While New Zealand cops suspected that the base had its own investigation, any results they uncovered were never shared with them.
The official verdict of New Zealand's coroner's report only said that Marks probably didn't know he was drinking methanol.
There was not enough evidence to rule out a prank, a suicide, or even foul play.
More mysteries
A number of theories have tried to explain Marks' sudden death, but nothing fits the facts.
One theory claims that he drank the methanol by accident in a drinking binge.
While Marks definitely was a drinker - he drank to hide his tourettes symptoms - he had his own stash of liquor, and was smart enough not to drink cleaning fluid.
Suicide is another common theory, but New Zealand detectives all but ruled it out.
"Dr. Marks had recently formed a close relationship with a woman at the base," their report read.
"He was active in his work and socially at the base. He had no financial worries and he was striving towards the completion of a significant piece of academic work."
There are also two mysterious loose threads in the dead scientist's case:
First, he had track marks his arms but was not known to use drugs.
Second, the station's doctor, Robert Thompson, has been missing since 2006.
As Rodney's father Paul says, we may never know just how Marks died.
"And I don't think we are going to try to find out any more in regards to how Rodney died," he explained. "I'd see that as a fruitless exercise."
Interested in cold cases? Here are even more mysterious stories:
