Two crowns and a jewelled orb were stolen from the Strangnas Cathedral in the western part of Stockholm on Tuesday morning (July 31).
Police said in a statement that they were alerted to the theft at 11.44am. The thieves snatched the priceless crown jewels and fled in a motorboat that was moored just below the cathedral, which is located near waters that flow into Lake Malar.
Police immediately began to search for the thieves by boat and in helicopters but were unable to capture them. In the statement, police described the motorboat as a small open boat, although it was uncertain what colour the boat was.
Investigations continued through the night, but by about 6am the next morning, police had not made any arrests.
Police spokesman Thomas Agnevik told Swedish newspaper Aftonbladet that the thieves broke the glass display case housing the jewels, which was armed with an alarm system.
Eyewitnesses told the Aftonbladet that two men were spotted fleeing from the cathedral.
The crowns were originally buried with King Charles IX in 1611, and later his wife Queen Christina, as their burial crowns. The crowns were later removed from the graves and placed on display at the cathedral.