(CNN)Sweden has ended a 34-year investigation into the unsolved murder of the country's then-Prime Minister Olof Palme, saying the chief suspect is dead.
Palme was gunned down as he took a late-night walk after visiting a cinema in central Stockholm with his wife, Lisbet, on February 28, 1986.
The mystery over the murder of the Social Democratic leader has gripped Sweden for three decades, prompting much speculation over the assassin and their motive, as well as producing multiple conspiracy theories.
Meanwhile, investigators have interviewed more than 10,000 people, and 134 possible suspects have confessed to the murder.
Sweden's Chief Prosecutor Krister Petersson told a news conference in the country's capital on Wednesday that he believed the lone perpetrator to be a man named Stig Engström but could do nothing more to prove it.
"As the person is deceased, I cannot bring charges against him and have decided to discontinue the investigation. In my opinion, Stig Engström is the prime suspect," he said.
"My assessment is that, after over 34 years, it is difficult to believe that any further investigation would provide us with any new details and therefore I believe we have come as far as one could expect."
Suspicion focuses on one man, whom investigators "cannot get around," he said. Engström, also known as "Skandia man" after the insurance company where he worked, died in 2000.
"To a large extent, we have been at the mercy of the police investigative work that was performed closer to the time of the crime," said Petersson.
"All in all, there are a number of circumstances that point to Engström. Had the current Palme investigation group been in charge 34 years ago, Engström would have been remanded in custody had he been unable to provide satisfactory explanations for his movements and actions. My assessment is that there would have been sufficient evidence to have him detained in custody."
False confessions, conspiracy theories
Speaking alongside Petterson, Hans Melander, head of the investigation, outlined the scale of the inquiry.
"It is by far Sweden's largest criminal investigation and is sometimes compared with the murder of JFK and [the] Lockerbie bombing. It has been ongoing since 1986 and contains 22,430 different points of interest," he said.
"Ninety-thousand people are included in the preliminary investigation, of which 40,000 are named. More than 10,000 people have been interviewed, many of them several times. More than 4,000 vehicles were investigated. And 134 people have confessed to committing the murder, including 29 directly to the police."
Analysis of the two bullets found at the scene -- one of which killed the Prime Minister, while the other injured his wife -- was carried out by laboratories in Sweden and Germany as well as by the FBI in the United States, he said.
But few traces were left on the .357 Magnum caliber metal-piercing bul