Joshua French and Tjostolv Moland at their appeal case in 2010 - Heiko Junge Scanpix
"They agree on what the cause of death is," Per Zimmer, a lawyer for the Norwegian Criminal Investigation Service told NTB. "I can not comment on what has come to light in the interests of the further investigations, and particularly the families."
Tjostolv was found dead in the cell he shared with fellow Norwegian Joshua French a week ago last Sunday.
On Monday evening, Norwegian authorities were still refusing to comment on what conclusion the Congolese investigators had come to, or on whether Moland's death was being treated as murder.
Congo's deputy foreign minister Tunda Wa Kasende speculated on Sunday that French had strangled Moland.
The two Norwegian ex-soldiers were sentenced to death in September 2009 for murdering their driver. Both have always denied guilt.
Norway's forensic examiner Arne Stray-Pedersen said that the authorities in Congo were now cooperating well with the Norwegian police who arrived last week.
"We have done thorough research and had a good relationship," he said. "We agree on the objective findings."