Police inspector Per Thomas Omholt told reporters the ongoing investigations had reinforced the idea that the suspect, Danish citizen Espen Andersen Brathen who has admitted the killings, had mental health issues.
However, “the thinking is that he did not take (the conversion) very seriously. By this we mean that he did not follow or practise the traditions that are common in this culture and religion,” the inspector said.
Website Nettavisen has published a video Brathen allegedly posted to social media in 2017, in which he issued a “warning” and declared his Muslim faith.
Four women and one man died, and three others were injured on Wednesday during the assault in the south-eastern town of Kongsberg.
It was Norway’s deadliest attack in a decade.
Brathen, 37, has been detained in a medical facility pending psychiatric evaluation.
“All the indications are that he chose his victims at random” and acted alone, Omholt said, describing Brathen as “not very social”.
The police also named the dead: Andrea Meyer, 52, Hanne Merethe Englund, 56, Liv Berit Borge, 75, Gunnar Erling Sauve, 75 and Gun Marith Madsen, 78.
The three people injured, who have not been identified, have all been released from hospital.