The mysterious death of champion Australian racehorse Phar Lap has been solved — more than 75 years after he died.

On Thursday (19 June) scientists confirmed that Australia’s greatest ever racehorse died from arsenic poisoning — solving the one of the longest running horseracing mysteries.

The winner of the 1930 Melbourne Cup Phar Lap died in mysterious circumstances at the Menlo Park racetrack in California in April 1932.

Phar Lap was found to be unwell by his handler Tommy Woodcock and in hours was dead.

Conspiracy theories were rife, with some saying the horse was killed by gangsters.

It was long suspected that Phar Lap had been poisoned, but this week hairs from the horse’s main were analysed by researchers Dr Ivan Kempson from the University of South Australia and Dermot Henry from the Natural Science Collections at Museum Victoria.

The hairs showed that 40 hours before the horse’s death, Phar Lap had ingested a fatal amount of arsenic.

But where the arsenic came from remains unanswered.

An accidental overdoes has long been suspected since notebooks kept by Phar Lap’s handler, Tommy Woodcock ,detail arsenic being used in various tonics and ointments given to the racehorse for stimulation. But that cannot be confirmed.

Phar Lap was a star of the Depression. The gelding won 37 of his 51 starts including Mexico’s Agua Caliente Hanicap, the then richest race in North America, just days before he died.