The man was suspected of plotting to kill Obid Nazarov, an imam highly critical of the Uzbek regime, who was shot in the head in Strömsund in north-western Sweden.
The Muslim cleric miraculously survived the attack, but fell into a two-year coma.
An Uzbek man was convicted in 2015 for the murder attempt, but the court ruled the attack was a contract killing and the prosecutor revealed a year later that another man had made several money transfers to the shooter and was suspected of being behind the plot.
However, in a documentary by Swedish public radio on Thursday, the prosecutor said he had decided to drop the investigation, having exhausted all possible leads in the case.
According to Interpol in Uzbekistan the suspect died in March 2017, which means that suspicions that the Uzbek regime was behind the plot are likely to go unsolved.
“The official version is that he is dead and I don't expect that I will be able to find this person, so until I get other information the preliminary investigation concerning him is closed,” prosecutor Krister Peterson told P3 Dokumentär.
“We have tried to look at other motives. Normally it's love, money, revenge, drugs, anything that can trigger someone's desire to kill someone else. But in this case we do not see that, it's a pure contract killing.”
Nazarov was granted political asylum in Sweden in 2006, after fleeing the Uzbek government's crackdown in Andijan.
After resettling in Sweden, he began serving as imam in the small Swedish town of Strömsund, with a population of just over 4,000.
A documentary aired by Uzbek state television in May 2010 accused Nazarov of masterminding a series of high-profile killings in 2009, as well as a 2004 suicide bombing at the US embassy.