Norwegian police on Thursday ended a six-day search for bodies on the island where anti-Islamist extremist Anders Behring Breivik killed 68 people and say they are increasingly certain he acted alone. Breivik, 32, killed a total of 76 people in a bomb attack in central Oslo followed by the shooting rampage at the island summer camp for the ruling Labour Party's youth wing. "The search at Utoeya [island] has been completed," police Chief-of-Staff Johan Fredriksen told a news conference. A search for bodies in the surrounding Tyrifjord lake was continuing. Police had received a number of bomb threats but that these were not considered credible, Fredriksen said . Police were trying to help Norwegians get back to normal after the trauma of the worst attack in their modern history. "In general we are trying to be visible to the public to try to contribute to the sense of security," he said. Dressed in a police uniform, Breivik massacred youths trapped on the island and shot at those who tried to swim to shore some 500 metres away, leading authorities to believe that a number may have drowned. Breivik has told police he was part of a network in his self-styled "crusade" against Islam and multiculturalism, but Norwegian authorities doubt this. "We have to consider the possibility but at this moment we have no indication of that," police lawyer Paal-Fredrik Hjort Kraby said. "He said in his manifesto that he was all alone and we are tying to find out if this is correct." Police will interrogate Breivik on Friday for the second time since he was arrested. The investigation has been conducted in cooperation with other European countries and the United States. The risk of copycat bombings remains low, police said, even though the attack comes amidst a rise in anti-immigrant sentiment in Europe as countries struggle to contain spiralling debt crises and revive flagging economies. "Europe has received a clear warning from Norway," wrote Thorbjoern Jagland, the former Norwegian prime minister who is now the leader of the Nobel Peace Prize committee and secretary general of the Strasbourg-based Council of Europe. "It's possible that Breivik has operated completely alone. But I'm afraid he may have initiated a new trend. While we've all been preoccupied with Muslims and radical Islam, this has been allowed to quietly develop," Jagland wrote in an article called "The racism in Europe" published by daily Aftenposten. "We see a new form of nationalism, in a new disguise. But the old wisdom is still valid: all nationalism comes from something bad and leads to something bad." Norway has promised a review of the country's security services and their actions during Breivik's attacks. Police have come under criticism, including from some survivors, for taking an hour to get to the island 42km from Oslo. On a pier jutting out from a campground across the lake from Utoeya, where some of the survivors first reached shore, mourners visit a memorial to lay flowers and pay their respect. Pictures and children's drawings adorn the site. One crayon drawing shows the green island and dozens of frowning faces in the waters around it. A letter placed between the flowers and candles starts "Dear Synne" and simply ends "I love you". "What happened here is not human," said social worker Heidi Weum Knutsen, looking out at Utoeya. "Young innocent people were hunted down and killed. That is the worst thing someone can do." Paramedic Haavard Larsen, who coordinated the health services response to the island shootings last Friday, said the survivors were completely silent when they made it to shore. "It's difficult to describe but if you saw old movies from concentration camps, that was a little bit their impression - empty looks, extremely traumatised," Larsen said. "One of my colleagues was trying to help a child ashore, and the kid stepped back and asked - 'are you going to shoot me?'" Clynical psychologist Therese Brask-Rustad, who helped treat the victim's families, said Breivik intentionally played on Norwegians' overwhelming trust in the police - which is broadly respected in this affluent and normally peaceful Nordic state. "He shattered their belief about who can be trusted. Shattered their assumptions about the world. It's a wonderful holiday island that became a nightmare."