COPENHAGEN, Denmark (AP) — A Norwegian man who killed his stepsister and then stormed an Oslo mosque and opened fire, harming no one, was found guilty Thursday and sentenced to 21 years, the longest allowed jail term under Norwegian law.

Philip Manshaus, who had said in court that he regretted not having caused more damage, “has proven to be an extremely dangerous person,” prosecutor Johan Oeverberg said as he demanded the maximum penalty.

Last year, Manshaus, 22, first killed his 17-year-old stepsister by shooting her four times with a hunting rifle at their home in the Oslo suburb of Baerum. Then he drove to a nearby mosque where three men were preparing for Eid al-Adha celebrations. Manshaus fired four shots from a rifle at the mosque's glass door before he was overpowered by one of the men in the mosque.

In court, Manshaus confessed to the acts but called them “emergency justice.”

One man was slightly injured when overpowering Manshaus.