Relatives of some of the 159 people who died when the Scandinavian Star ferry caught fire on its way from Oslo to Frederikshaven in Denmark, have long campaigned for the case to be reopened, arguing that there is evidence to suggest that the fire was a deliberate arson carried out by the ship's crew.
Oslo police chief Hans Sverre Sjøvold last year tasked a special committee with looking at the original investigation carried out in the aftermath of the fire in 1990.
"Their report shows in my opinion that some parts of the case were not sufficiently well illuminated," Hans Sverre Sjøvold, the chief of the Oslo police, said in a statement on Friday.
"Although there are no new findings in the case, I have on the basis of their overall assessment nonetheless decided to recommend a new investigation of these parts of the case."
Sjøvold said that the group's review of the evidence showed that the possible financial motives of the Vognmandsruten, "had not been investigated sufficiently", and that the evidence which the original report used to pin the fire on Erik Mørk Andersen, a Danish truck driver, had been "inadequate".
"If a similar fire had occurred today, those motives would have routinely been investigated," he said. "In addition, it appears that the evidence pointing to the Danish citizen as the perpetrator was inadequate."
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In 2013, a report of independent experts concluded that the Danish driver had died of asphyxiation before the last of the four fires on the boat was lit.
A previous 2009 investigation concluded that the fires on the boat could not conceivably have been lit by a single person, particularly one, like the Danish man, with little knowledge of the layout of the boat.