The Norwegian Supreme Court on Friday increased the sentences of two men convicted in the theft of Edvard Munch masterpieces The Scream and Madonna and ordered a new trial for a third convicted man.

The paintings, which are considered priceless, were stolen in August 2004 in a daylight raid on the Oslo city-owned Munch Museum. They were recovered by police nearly two years later, and are undergoing repairs for scrapes, punctures, loose paint, and moisture damage.

Edvard Munch's masterpieces Madonna and The Scream were damaged in the 2004 theft.
(Richard Jeffries/Scanpix/Munch-Museet/Associated Press)

All three men appealed their April 2006 sentences from a lower court, which ranged from five to 9½ years, last month.

In its unanimous 12-page ruling, Norway's highest court said sentences for two of the men, Petter Tharaldsen and Stian Skjold, were too low considering the "irreplaceable national cultural value" of the paintings.

"The sentence should therefore be somewhat higher … than if it had been the theft of money of the same economic value," said the Oslo court, which is a final ruling for the two.

The paintings are insured for $141 million US, but experts say their real value cannot be estimated. 

The court increased Tharaldsen's sentence by one year to 10½ years, and Skjold's sentence by six months to six years. Under Norwegian law, higher courts frequently increase sentences when considering appeals.

But the court rejected the conviction of a third man, Bjoern Hoen, who had been sentenced to 5½ years in prison, saying testimony in his trial may have been tainted, and sent his case back to the lower courts for a new trial.

Two of the key witnesses against Hoen, including a police informant, had agreed to work together on a book about the thefts without informing the courts or the defence attorneys of their plans.

The Supreme Court wrote that testimony by those two witnesses "could have been judged differently if the court had been given information about the book project, with consequence being that the question of guilt or sentencing being evaluated in a different way."

Munch's emotionally charged painting style became a major influence in the birth of the 20th-century Expressionist movement. Munch died in 1944 at the age of 80.