Anders Behring Breivik (32), a Norwegian citizen of Norwegian descent, was arrested after the two attacks.
It appears he is lined with with right-wing political activists but the motive for the two attacks is still unknown.
Late Friday on night police searched Breiviks apartment in Oslo. The 32-year-old man will be questioned by the police Saturday.
The first reports of the massacre on Utøya, an island about north-west of Oslo, came around 18.25 Friday.
According to a witness the gunman claimed to be a police officer offering help, before he opened fire and started killing people.
Nearly 700 young members of the Labour Party were on the island for an annual youth camp.
It took a while for the police to realise the full extent of the massacre. Saturday afternoon police confirms that at least 85 people are killed in the shootings on the island.
Some of the youth tried to swim to safety to escape the gunman.
The death toll may rise even more as rescue workers search the water around the island.
Yesterday police said they also found explosives in a car on the island.
The shootings on Utøya came only hours after a bomb exploded outside a government building in central Oslo at 3.26 PM Friday.
The explosion killed at least seven people and further ten people are seriously injured in the blast, confirms police. So far only four people have been identified.
A man dressed as a police officer was also seen at this scene.
Surrounding buildings were affected by the massive explosion close to Prime Minister Jens Stoltenberg's office. He was not at his office at the time, and was not injured.
Several blocks around the bomb are still evacuated and people are asked to stay away from the city centre.
Premier: "You will not destroy us"
"We will find those responsible and hold them accountable", said the Norwegian Prime Minster Jens Stoltenberg at a press conference late Friday.
He also had a message to the people behind the attacks
"You will not destroy us. You will not destroy our democracy or our ideals for a better world."