Police inspector Per Thomas Omholt said it was likely that the suspect, Espen Andersen Braathen, first used arrows to wound his victims and then killed them by stabbing them with an unspecified weapon in Wednesday's attack in Kongsberg.
"When it comes to weapons, we have previously stated that a bow and arrow has been used," Omholt told reporters Monday. "Other weapons that have been used are stabbing weapons. We don't want to go out with what kind of stabbing weapons were used as all witnesses at the scene haven't been questioned yet."
Andersen Braathen, a 37-year-old Danish citizen, has confessed to the killings and has initially been charged with five murders. Omholt said, however, that the list of charges would be extended as the investigation proceeds.
Norwegian police have identified the four female victims as Andrea Meyer, 52; Hanne Englund, 56; Liv Berit Borge, 75; and Gun Marith Madsen, 78. The male victim was Gunnar Erling Sauve, 75. Meyer is a native of Germany who had moved to Norway several years ago.
"So far, all indications are that these victims were randomly picked," Omholt said, adding that police had questioned some 60 witnesses.
The regional police department received reports Wednesday evening about a man shooting arrows at the Coop Extra supermarket in central Kongsberg, a sleepy town of about 26,000 residents.
An unarmed police patrol spotted the suspect in the supermarket and Andersen Braathen shot at them with several arrows before fleeing. One of the wounded was an off-duty police officer inside the supermarket. The patrol called for reinforcements and armed police apprehended the suspect, but not before the victims were killed, police said.
Norway's domestic intelligence agency has called for an independent investigation into the police's delay in capturing Andersen Braathen amid criticism that the police response was too slow.
The Associated Press contributed to this report.