Of the robbers who stormed into Oslo's Munch Museum in August 2004, only one was thought to have attended the court session Tuesday; police said they think the other robber died, Aftenposten said.
The one who died is considered the ringleader, police said.
Appealing their convictions were Bjorn Hoen, 38 and Petter Rosenvinge, 39.
Attorneys for the defendants petitioned to have the appeals trial postponed, saying they hadn't been allowed to review an agreement negotiated by police that led to the recovery of the paintings.
The attorneys asked Norway's Supreme Court to intervene and order the secret files released, but the high court has not responded. The defense attorneys said they wanted the case delayed until the Supreme Court reached a decision; the refusal means the trial will proceed.
The defendants are appealing prison terms handed down last year in connection with the art heist. They're also appealing the compensation claims they were ordered to repay to the city of Oslo to cover costs associated with the theft.