A decades-long criminal investigation compared in scale to the probe into the assassination of President John F. Kennedy and the Lockerbie bombing has ended with the case unsolved as investigators said they were calling off the hunt for answers to the 1986 killing of then prime minister, Olof Palme.

Swedish prosecutors attracted worldwide attention when they announced Wednesday they would reveal the results of their investigation into the killing, which has fascinated Sweden for 34 years and become the subject of florid conspiracy theories.

But those looking for answers were disappointed: the prosecutor’s office said it was discontinuing the investigation because their main suspect, Stig Engström, killed himself in 2000.

Palme was aged 59 when he was shot in the back on a busy Stockholm street while returning from a movie theater. Supporters credit him with forging the image of modern-day Sweden, still vaunted globally today.

Some 90,000 people have worked on the murder case. It has generating countless conspiracy theories, with alleged suspects ranging from Kurdish militias and Indian arms dealers to South Africans angry about Palme’s stance against apartheid.

“Because that person is dead, I cannot bring charges against him but decided to close the preliminary investigation,” prosecutor Krister Petersson said in a briefing.

Engström had become well known as a suspect in the case and was nicknamed the “Skandiamannen” because he worked at the nearby Skandia insurance company. He was one of the first people at the scene and claimed that he had attempted to resuscitate Palme, whose policies he was known to strongly oppose.

“Stig Engström wasn’t a focal point on the investigation but we’ve looked at his background, and what we can see there is that he was used to using weapons, he had been employed by the army and was a member of a shooting club,” the prosecutor said. His movements on the night of the murder were “consistent with how we believe the perpetrator has acted that evening” and he was known to have financial and alcohol problems, he said.

Palme’s wife, Lisbet, was injured in the attack and later identified the shooter as Christer Pettersson, an alcoholic and drug addict, who was convicted of her husband’s murder and later died in 2004.

The sentence was later overturned after police failed to produce any technical evidence against him, leaving the murder an unsolved mystery.

The Associated Press contributed to this report.