Olof Palme, a populist, left wing politician whose views made him numerous enemies at home and abroad, was shot in February 1986 as he walked home with his wife from a cinema in Stockholm. More than 30 years of inquiries has seen the focus fall on everyone from South African agents — Palme was a vocal critic of apartheid — to rogue Swedish spies.

Stieg Larsson helped police with the investigation — has taken yet another twist after it emerged that a key suspect no longer has an alibi for the night in question.

The South African link

Steig Larsson — the late author of the hugely successful Millennium trio of crime thrillers, and an expert on far-right groups — left 15 boxes of files connected to his own probe into the case. Larsson passed police the name of Bertil Wedin, a Swede with links to South African security services, as the man who organised the killing. Wedin, now living in northern Cyprus, denies this and police said he is not a suspect.

The right-wing nutter

A Swedish newspaper says another right-wing activist, who was an associate of Wedin, did it. Alf Enerstrom, a doctor and implacable right wing opponent of Palme who spent time in a psychiatric hospital after shooting a policewoman, was investigated closely by police but always maintained that at the time of the killing he was at home with his then-partner — an account she backed up.

The Yugoslav connection

Germany’s Focus magazine in 2011 cited official German interrogation records that said the murder had been carried out by a contract killer hired by the then Yugoslavian security service. Yugoslavian hit man Vinko Sindicic claimed he knew the killer. The motive was Palme’s opposition to Yugoslav arms sales

The PKK and the Kurds

Another popular theory was that Palme was assassinated by the Kurdistan separatist group PKK. The Stockholm police commissioner at the time was a supporter of the theory — although it ultimately led to his dismissal from the investigation. In April 2011, a team of Swedish police officers interviewed jailed PKK leader Abdullah Ocalan about a Kurdish connection.

Swedish security services

The German weekly Die Zeit ran an article by Klaus-Deieter Knapp in 1995 which presented the murder as a conspiracy by Swedish right-wing extremist police officers. They were supposedly motivated by Palme’s opposition to closer ties with the US, where President Ronald Reagan had stepped up pressure on the Kremlin.

Christer Pettersson

This petty criminal and drug addict, who was identified by Palme’s widow, was tried and convicted of the murder but later acquitted on appeal to the High Court. Evidence against him resurfaced in the late 1990s but was not enough to prove his involvement. A documentary aired on STV in 2006 featured several associates of Pettersson claiming that he had confessed.

Apartheid South Africa

Former South African police officer Colonel Eugene de Kock said in September 1996 that Palme had been killed because he “strongly opposed the apartheid regime and Sweden made substantial contributions to the ANC [African National Congress]”. De Kock named Craig Williamson, a former police colleague and a South African agent, as the assassin but no proof was ever uncovered.

Israel and Mossad

Conspiracy theorists suggest Mossad killed Palme for his continued support of Yasser Arafat and the Palestine Liberation Organisation, and his support of anti-Israeli policies. Palme was also a vocal supporter of the Polisario cause in Western Sahara.