The riddle of the mysterious death of New Zealand's most famous racehorse may have been solved more than 75 years after his death.
Phar Lap probably died as a result of arsenic administered by his own trainer, rather than being murdered by American gangsters as Dowunder fans have long believed.
That is the conclusion of experts who have studied a "recipe book" of tonics used by Phar Lap's trainer, Harry Telford, which sold at auction on Thursday in Melbourne for A$37,000 ($44,000).
The ingredients the tonics contained were arsenic, strychnine, belladonna, cocaine and caffeine - once given to horses in small quantities as stimulants, before a race.
Phar Lap, a chestnut gelding was born in Timaru, died at the Menlo Park Race Track in California in 1932 when he was five years old.
He was at the peak of his career, having won 37 of his 51 races including the 1930 Melbourne Cup.
Two weeks before his sudden and agonising death, he had won North America's richest race, the Agua Caliente Handicap in Mexico.
Fans were horrified by the news, and conspiracy theories involving foul play abounded.
The most enduring one was that "Big Red", as he was known, was poisoned by gangsters who - because he appeared to be unbeatable - feared he would upset their illegal gambling syndicates.
Telford did not go with Phar Lap on his first trip to the US.
Instead, Tommy Woodcock, his stand-in trainer, travelled with him.
But Woodcock took Telford's 82-page handwritten book of tonics with him, and he may have accidentally given the champion a fatal overdose.
Auctioneer Charles Leski, of Charles Leski Auctions, said this week: "It's the first time that we have had, in writing, confirmation that caffeine, cocaine, belladonna, strychnine - all of them we think of as poisons - were actually used by Harry Telford in the maintenance of his horses.
"In strictly measured doses, and mixed in with other feed, presumably these served the purpose of being a stimulant and didn't adversely affect the horses.
"But if Phar Lap had been unwell during the trip over to America, or if he had been in the hands of more than one person in the US, it's possible the dosage wasn't strictly adhered to, and it appears he overdosed on a concoction that was considered good for him."
The notebook, which contains 30 recipes, was bought by the Melbourne Museum, which has displayed Phar Lap's hide since 1933, as well as his saddle and other memorabilia.
His skeleton is in Te Papa Museum and his massive 6.3kg heart is in Canberra's National Museum.
The thoroughbred gelding collapsed at his stables soon after travelling back to the United States from Mexico.
Woodcock found him in severe pain, with a high temperature, and a few hours later he died of internal bleeding.
A postmortem examination revealed the horse's stomach and intestines were inflamed, which triggered theories that he had been poisoned.
Tests in 2006 on a strand on his hair, taken from his hide, suggested Phar Lap had ingested a large amount of arsenic about 35 hours before he died.
But racing experts believe that the arsenic is more likely to have built up gradually over a period of time.
The days before swabbing, it was common for racehorses to be fed small quantities of arsenic, to give them an edge.
A popular tonic of the day was Fowler's Solution, which was arsenic-based and was administered to Phar Lap throughout his racing career. Repeated doses might have accumulated in his body and eventually proved deadly.
Dr Percy Sykes, a contemporary racehorse trainer , said after the tests in 2006: "I wouldn't be surprised if arsenic was found in every horse in that era."
Telford admitted on his deathbed in 1985 that the horse might have died from consuming an excessive quantity of one of his tonics.
The notebook is the first written proof of the ingredients found in the tonics.
Phar Lap was a source of pride to Australians and New Zealanders during the Depression and is still regarded as a heroic figure.