Police in Norway said that the man being questioned for killing at least 98 people in a bomb blast in Oslo and a shooting on the nearby island of Utoya gave himself up when police arrived.
Police chief Sveining Sponheim said at a press conference that the man was able to shoot victims for more than an hour and a half and that the special forces had found it difficult to get to the island, but that "it was not dramatic" when he was arrested.
"When the special forces came to the island he gave himself up," Sponheim said through a translator.
The death toll, which currently stands at 98 from the two incidents, could still rise and that four or five people were still missing.
The attack in Oslo was confirmed to have been the result of a car bomb. Police said that human remains were still being retrieved from the government buildings in central Oslo.
There had been suggestions than witnesses had reported a second gunman on the island, but the police said that was still being determined.
Police interviews will continue until at least Monday, the police chief said, and the man is expected to be formally charged on Monday.
Earlier, Norway's Prime Minister said that his "childhood paradise had been transformed into hell" by the attacks.
At a press conference on Saturday morning PM Jens Stoltenbeg said that the attacks were a "national tragedy".
"Never since the Second World War has our country been hit by a crime on this scale," he said.
The suspected attacker, who has been named as Anders Breivik by Norwegian media, is a blond, blue-eyed Norwegian man.
Click Here For a Full Profile Of The Suspect
It is reported that the attacker was dressed as a police officer when they opened fire on young people attending a summer youth camp for the country's Labour party.
Panicked victims reportedly tried to hide and run into the water surrounding the island, but were fired upon from the shore in an attack that may have lasted for more than an hour before a man was apprehended.
The shootings followed an explosion in central Oslo that killed at least seven people. Police said that the bomb was set off by the same suspect.
Prime Minister David Cameron said that the UK would do all it could to help.
"These attacks are a stark reminder of the threat we all face from terrorism. I have called Prime Minister Stoltenberg this evening to express my sincere condolences and to let him know that our thoughts are with the Norwegian people at this tragic time."
"I have offered Britain's help, including through our close intelligence cooperation. We will work with Norway to hunt the murderers who did this and prevent any more innocent deaths. We can overcome this evil, and we will."
The two attacks represent the worst combined day of violence in Western Europe since the 2004 bombings in Madrid that killed 191 people.