Anders Behring Breivik, the principal suspect in the twin terror attacks in Norway last Friday, may undergo compulsory medical treatment following a medical examination, a Swedish law expert said on Wednesday.

Lawyer Bernt Birkeland said if the medical exam proves that Breivik was insane, he would be put into a mental institution for compulsory treatment, but if he was mentally stable he could be sentenced to life in prison.

Breivik's lawyer, Geir Lippestad, said on Tuesday that "this whole case indicated that he [Breivik] is insane."

Norwegian Prosecutor Christian Hatlo said on Tuesday that if charged with crimes against humanity, Breivik could face up to 30 years in prison. In line with the laws in Norway, a court's verdict could be revised as many times as possible and therefore the prison sentence could be prolonged as well.

During a closed hearing at a Norwegian court on Monday, Breivik, 32, admitted to carrying out a bombing in Oslo that killed seven people, and a mass shooting at a Labor Party youth camp on the nearby island of Utoya.

Police have now revised the death toll from both attacks from 93 to 76.

The Norwegian telegraph bureau reported on Wednesday that Brevik was a member of a gun club in Oslo between 2005 and 2007 and from June 2010 until recently.