The shot rang out in a busy street in Stockholm in February 1986, fired at point-blank range. Less than an hour later, the prime minister of Sweden was pronounced dead.
But 37 years and multiple investigations later, including a decade-long probe by famed crime writer Stieg Larsson, nobody has ever been brought to justice for Olof Palme’s murder.
Now a new four-part series from Sky Documentaries explores the unsolved assassination sometimes known as “Europe’s JFK shooting”, and the world of spies and intrigue that swirls around it.
Jan Stocklassa is a former diplomat for the Swedish foreign ministry who has spent the last 10 years investigating Palme’s murder.
He was doing research for a book when he came across a trove of materials compiled by Larsson, the author of The Girl With The Dragon Tattoo, who had quietly spent years trying to find the killer before he died in 2004.
“The murder of Olof Palme has been on and off in people’s minds for 37 years,” Mr Stocklassa tells Sky News.
“It’s always there, and it’s sort of a wound that starts to heal and then gets torn up again.”
The assassination came at a time when, as leader of Sweden, Palme was walking a dangerous tightrope between the two superpowers: the US and the Soviet Union.
The USSR was eyeing expansion – something America and the West were desperate to keep Sweden away from due to its geographical and strategic importance.
Controversially, Palme sought to keep Sweden as a neutral, non-aligned country and, crucially, one that was not in NATO.
So it was at a delicate time for Sweden that Palme was assassinated, possibly changing the course of his country’s history.
“The political situation changed a lot and I don’t think we realised it then”, Mr Stocklassa said. “Sweden was trying to create this third possibility between the Soviet Union and the US and help all small nations to be able to run their own destiny.
“And that one bullet in the back of Olof Palme has changed that immediately.”
Now, following the Russian invasion of Ukraine, Sweden has abandoned its decade’s long position of neutrality and is set on joining NATO.
‘Historic moment’ as Sweden applies to join NATO
NATO allies ‘agree Ukraine will become member’
Mr Stocklassa’s investigations into Palme’s murder saw him enter a world of shadowy intrigue and even come face to face with former spies. What was that like?
“Scary,” he says. “I went to Cyprus to meet this Swedish spy living in northern Cyprus because he wanted to avoid extradition.”
Mr Stocklassa says he used a fake name to meet the spy and didn’t know who to trust, even the police.
But he said entering the world of spooks was a “rush” that you can get “drawn into or addicted to”.
After a decade of research, Mr Stocklassa says the assassination still remains unsolved – but he says he has built on Larsson’s work and has a theory.
“I’m not saying who I believe was actually pulling the trigger, I have a theory on that,” he says.
“But more importantly, you can see the actual forces behind it, with the South Africans using a Swedish middleman and using Swedish right-wingers as helpers and possible scapegoats or patsies.
“That’s the theory that Stieg (Larsson) believed in, and I strongly believe in. I’m even convinced about it.”
The Man Who Played With Fire returns for episode two on Sunday, 21 May on Sky Documentaries and Now. Episode one is available to watch on catch up.