The search for both the culprits and the jewels gained international attention after 17th-century royal crowns were taken from a cathedral in Strängnäs, one hour from Stockholm, with the suspects then seen fleeing the scene by bicycle and motorboat.
The suspect told the court: “It was me who carried out the theft” after his lawyer earlier said that the man had confessed to being guilty of aggravated theft.
The stolen jewels were found in early February by a security guard who discovered them atop a rubbish bin north of Stockholm.
After police confirmed that these items were in fact the missing crowns, they found traces of the 22-year-old's DNA on the jewels. He was already on trial after being identified by blood found at the crime scene, but during the initial police investigation had denied any involvement in the heist.
The crowns were made for the burial of King Charles IX and his wife Christina and date back to the early 1600s. They were stolen along with a royal orb.
A further two men, aged 24 and 26, have also been detained on suspicion of aggravated receiving of stolen goods.
July's royal heist was the second to take place in the area around Lake Mälaren in recent years.
In 2013, a crown and sceptre used in the funeral of Sweden's King Johan III were stolen from nearby Västerås. Those items were later located in two large rubbish bags at the side of a highway following a tip-off to police.