SUNDVOLLEN, Norway (Agencies) - Norway mourned on Sunday 93 people killed in a shooting spree and car bombing by a Norwegian who saw his attacks as atrocious, but necessary to defeat liberal immigration policies and the spread of Islam. In his first comment via a lawyer since his arrest, Anders Behring Breivik, 32, said he wanted to explain himself at a court hearing Monday about extending his custody. He has said that he believed the actions were atrocious, but that in his head they were necessary, lawyer Geir Lippestad told independent TV2 news, adding that Breivik had admitted to Fridays shootings at a Labour party youth camp and the bombing in Oslos government district earlier the same day. Oslos acting police chief Sveinung Sponheim confirmed to reporters that Breivik would be able to speak to the court. It was not clear whether the hearing would be closed or in public. He has admitted to the facts of both the bombing and the shooting, although hes not admitting criminal guilt, Sponheim said, adding that Breivik had said he acted alone. Police were checking this because some witness statements from the island spoke of more than one gunman, Sponheim said. Armed police detained several people in a raid on a small house attached to a warehouse in northern Oslo, a police lawyer told Reuters. They were later released and had no link to Fridays attacks. No explosives were found in the raid. Police chief Sponheim confirmed that Breivik had published a 1,500-page anti-Islamic manifesto Friday just hours before the attacks. The online tract, written in English, describes how he planned his onslaught and made explosives, as well as outlining his violent philosophy. The killings would draw attention to the manifesto entitled 2083-A European Declaration of Independence, Breivik wrote. Once you decide to strike, it is better to kill too many than not enough, or you risk reducing the desired ideological impact of the strike, he wrote. He attacked what he called the Islamic colonisation and Islamisation of Western Europe and the rise of cultural Marxism/multiculturalism. Sponheim defended the speed of the police response to the massacre on the island, only 500 metres long, where the gunman was able to shoot unchallenged for a prolonged period. The response time from when we got the message was quick. There were problems with transport out to the island, he said. Witnesses said the gunman shot his victims at will, as youngsters fled in panic or tried to swim to the mainland. Breivik may have intended the Oslo bombing, which killed seven people, partly as a diversion. Police believe he drove to Utoeya after the explosion in the capital. His lawyer, Lippestad, speaking late Saturday, did not give more details of Breiviks possible motives. A 12-minute video clip posted on YouTube with the same title as the manifesto featured symbolic imagery of the Knights Templar and crusader kings as well as slides suggesting Europe is being overrun by Muslims. Before we can start our crusade we must do our duty by decimating cultural Marxism, said a caption under the video on YouTube, which removed the clip Saturday. Police could not confirm that Breivik had posted the video, which also featured photographs of him dressed in a formal military uniform and in a wet suit pointing an assault rifle. The video was a series of slides that accused the left in Europe of allowing Muslims to overrun the continent: One image showed the BBCs logo with the C changed into an Islamic crescent. Another declared that the end result of the lefts actions would be an EUSSR. Police spokesman John Fredriksen confirmed that the essay was posted the day of the attacks. The document signalled an attack was imminent: In order to successfully penetrate the cultural Marxist/multiculturalist media censorship, we are forced to employ significantly more brutal and breathtaking operations, which will result in casualties. Norway has long been open to immigration, which has been criticised by the populist Progress Party, to which Breivik once belonged. The Labour Party, whose youth camp he attacked, backs multi-culturalism to accommodate different ethnic communities. We are all in sorrow, everybody is scared, said Imran Shah, a Norwegian taxi driver of Pakistani heritage, as a light summer drizzle fell on unusually empty Oslo streets. Home-grown anti-government militants have struck elsewhere, notably in the United States, where Timothy McVeigh killed 168 people with a truck bomb in Oklahoma City in 1995. Breiviks actions have prompted soul-searching in Norway. At Oslo cathedral, Britt Aanes, a priest aged 42 said the fact that Breivik was Norwegian had affected people deeply.