Eric Torell, who had the mental age of a three year-old, died in a hail of bullets after sneaking out of his home in Stockholm in the middle of the night to play.
Police fired 25 shots at Torell in a residential courtyard believing a toy pistol he was carrying was a real weapon. Torell, was hit three times. Two of the shots, including the one that killed him, hit him in the back.
"I have decided that the police who have been charged for the shooting did not follow the procedures they should have done and had they done so, they would have realized that Eric - the victim - was not a threat," prosecutor Martin Tiden told reporters.
Two officers were charged with misconduct and one with causing another person's death.
Tiden said the police were justified in opening fire at Torell, who did not respond when asked to put down his gun, but that they should have stopped firing when Torell turned away from them.
Torell's death caused a public outcry and raised questions over the use of deadly force by Swedish police.
"I hope that we get clarity about what happened, how it could go so wrong and that they change the way police are trained because this can't be allowed to happen," Torell's mother told news agency TT.
Officers have shot and killed an average of one person per year over the last 20 years, according to police statistics.
But numbers have been increasing with six people shot to death in 2018 and an average of 3.2 over the last five years.
In the United States, 992 people were shot dead by police in 2018, according to the Washington Post's database. The population of the United States is about 330 million against Sweden's 10 million.
In the United Kingdom, which has a population around 60 million, four people were shot to death by police in 2017-18 and six in 2016-17, according to government statistics.Sweden's National Police Commissioner Anders Thornberg has asked the government to review the rules surrounding the use of firearms.