No direct evidence was presented but the prosecutor mentioned Engström's past knowledge of weapons, friendship with anti-Palme circles and similar clothes as described by certain witnesses.

Walking home from the Grand Cinema with his wife Lisbeth Palme on the central Stockholm street of Sveavägen, close to midnight on 28 February 1986, the couple were attacked by a lone gunman.

[7] Instead, several opposition figures from those countries were invited, such as South African anti-apartheid fighters Desmond Tutu and Allan Boesak, and Chilean politician Gabriel Valdés, an opponent of the dictatorship of Augusto Pinochet.

From the bullets' lack of certain characteristic deformations, investigators concluded they had been fired from a barrel no shorter than 10 cm (4 inches); thus the murder weapon would have been a conspicuously large handgun.

The person who stole the weapon was a friend of drug dealer Sigvard "Sigge" Cedergren, who claimed on his deathbed that he had lent a gun of the same type to Christer Pettersson two months prior to the assassination.

This weapon, a revolver of the type Smith & Wesson Model 28 ("Highway Patrolman") with .357 Magnum caliber, was first purchased legally by a civilian in the northern Swedish city of Luleå.

A police sketch of the supposed killer was widely circulated in the media a week after the murder, leading to a massive influx of tips from the public, but it was later determined that the witness on whose statement it was based probably had not seen the actual assailant.

The chief prosecutor, Agneta Blidberg, considered re-opening the case, but acknowledged that a confession alone would not be sufficient, saying: He must say something about the weapon because the appeals court set that condition in its ruling.

According to a documentary programme broadcast on Swedish state television channel SVT in February 2006,[citation needed] associates of Pettersson claimed that he had confessed to them his role in the murder, but with the explanation that it was a case of mistaken identity.

Allegedly, Pettersson had intended to kill Sigvard Cedergren, a drug dealer who customarily walked along the same street at night and resembled Palme both in appearance and dress.

In the newspaper Dagens Nyheter of 28 February 2006, other SVT reporters scathingly criticized the documentary, alleging that the film-maker had fabricated a number of statements while omitting other contradictory evidence, in particular his chief source's earlier testimony that could not be reconciled with his claim to have seen the shooting.

"[36] Ten years later, towards the end of September 1996, Colonel Eugene de Kock, a former South African police officer, gave evidence to the Supreme Court in Pretoria, alleging that Palme had been shot and killed because he "strongly opposed the apartheid regime and Sweden made substantial contributions to the ANC".

[39] A few days later, former police Captain Dirk Coetzee, who used to work with Williamson, identified Anthony White, a former Rhodesian Selous Scout with links to the South African security services, as Palme's actual murderer.

[40] Then a third person, Swedish mercenary Bertil Wedin, living in Northern Cyprus since 1985, was named as the killer by former police Lt. Peter Caselton, who had worked undercover for Williamson.

[40] The following month, in October 1996, Swedish police investigators visited South Africa, but were unable to uncover evidence to substantiate de Kock's claims.

A book that was published in 2007 suggested that a high-ranking Civil Cooperation Bureau operative, Athol Visser (or 'Ivan the Terrible'), was responsible for planning and carrying out Olof Palme's assassination.

[41] The 8 September 2010 edition of Efterlyst, Sweden's equivalent of BBC TV's Crimewatch programme, was co-hosted by Tommy Lindström, who was the head of Swedish CID at the time of Olof Palme's assassination.

After being asked by Efterlyst's host Hasse Aro who he believed was behind the assassination of the Prime Minister, Lindström without hesitating pointed to apartheid South Africa as the number one suspect.

Bondeson's book meticulously recreated the assassination and its aftermath, and suggested that Palme had used his friendship with Rajiv Gandhi to secure a SEK 8.4 billion deal for the Swedish armaments company Bofors to supply the Indian Army with howitzers.

Bondeson theorized that Palme's murder might have been inadvertently triggered by his conversation with the ambassador, if either the Bofors arms dealers or the middlemen working through AE Services had a prearranged plan to silence the Prime Minister should he discover the truth and the deal with India become threatened.

[43] Another plot sees the involvement of the CIA and the Italian clandestine, pseudo-masonic lodge Propaganda Due led by Licio Gelli who wrote, in a telegram to Philip Guarino, that "the Swedish tree will be brought down".

[44][45][46] Claims of CIA involvement in the assassination were made by Richard Brenneke, an Oregon businessman who said he was an ex-CIA operative, in a RAI Television report in July 1990.

[50] He refused to submit his gun, the only registered .357 caliber weapon in the Stockholm region not to be tested, and subsequently claimed to have sold it to an unknown buyer in Kungsträdgården.

[citation needed] In an article in the German weekly Die Zeit from March 1995, Klaus-Dieter Knapp presented his view of the assassination as a result of a conspiracy among Swedish right-wing extremist police officers.

"[52] Following up on this suggestion, Hans Holmér, the Stockholm police commissioner, worked with an intelligence lead passed to him (supposedly by Bertil Wedin) and arrested a number of Kurds living in Sweden.

Pettersson proposes Engström's media appearances were an opportunistic and ultimately successful tactic devised to mislead investigators and later to gain attention as an important witness neglected by the police.

While Pettersson's theory is built on circumstantial evidence, he suggests it might be possible to prove Engström's guilt conclusively by tracing and examining the murder weapon.

The "Skandia man" theory had already previously been suggested by Lars Larsson in his 2016 book Nationens fiende[64] (literally, "The enemy of the nation"), but this received only limited attention at the time.

[65] Although Engström had a negative view of the prime minister, as well as long-standing financial and growing alcohol problems, investigators still did not have a "clear picture" of Engstrom's motive for killing Palme, Chief Prosecutor Krister Petersson said.

In the 2021 Netflix series The Unlikely Murderer, Palme's assassin was depicted as Stig Engström, the so-called "Skandia man," based on the book by Thomas Pettersson.