Joshua French and Tjostolv Moland at their appeal case in 2010 - Heiko Junge Scanpix
"The investigation ended today concludes that there is no reason to believe that the death was a crime of any kind," Major Tim Mukuntu, said on Wednesday, citing the lack of any evidence of physical violence on the body. "All the indications are that Moland took his own life."
Moland's cell-mate Joshua French said he was relieved that the authorities had dropped the "absurd" claim that he had himself strangled his countryman.
"That was the most important thing for me," he said.
French, 31, found his friend dead in their shared cell earlier this month, adding new impetus to Norwegian authorities' efforts to bring him home.
Moland, who was 32, and French, a dual Norwegian-British citizen, were arrested in DR Congo in 2009 and sentenced to death in June 2010 after being convicted of killing the Congolese driver of a car they had rented.
Norwegian police sent a team of four to help investigate the death. Diplomats are now trying to bring Moland's body home and negotiate French's transfer to a prison in Norway.
"Now we are going to put everything into a diplomatic solution to get French home," his lawyer Marius Graasvold told Norway's NTB on Tuesday night.