Kai Eide, who served as the United Nations' special representative in Afghanistan, on Friday met Joshua French, the Norwegian former soldier who has been jailed in the country since 2009.
"He seemed in good spirits and is in good shape considering to he has been jailed in a Congolese prison for over four years," Eide told VG newspaper after his 45-minute meeting.
French was on Tuesday charged by Congolese authorities for murdering his former cellmate, friend and business partner Tjostolv Moland, with police claiming that he first drugged him with sleeping pills and then strangled him while he slept.
The charges came despite a joint Norwegian-Congolese investigation concluding in August that Moland had probably committed suicide.
"We do not understand the indictment, given that Norwegian police conducted a joint investigation and post mortem following Moland's death," Svein Atle Michelsen, a spokesman for Norway's Foreign Ministry, told Reuters. "Congolese and Norwegian police reached a joint conclusion that there was no indication of foul play or criminal activity."
Congolese police now accuse French of drugging Moland with sleeping pills before choking him. VG newspaper reported that the Norwegian blood samples showed that Moland had consumed alcohol, not sedatives.
Eide also met with Congolese authorities on Friday and now aims to meet with senior Congolese politicians to try and broker a solution.
"I want of course to get a meeting with the Congolese authorities at as high a level as possible," he told VG.
French and Moland were arrested in Congo in 2009 and later found guilty of murdering their driver Abedi Kasongo. Both have always denied any guilt.