Anders Behring Breivik, 32, seen in an undated photo taken...

Anders Behring Breivik, 32, seen in an undated photo taken from Facebook.com, is the central suspect in the shooting attack on the Norwegian island of Utoya that killed some 90 people on July 22, 2011. Credit: Getty Images

The Norwegian man suspected in a bombing and shooting spree that killed at least 92 people bought six tons of fertilizer before the massacre, the supplier said Saturday as police investigated witness accounts of a second shooter.

Norway's royal family and prime minister led the nation in mourning, visiting grieving relatives of the scores of youth gunned down at an island retreat, as the shell-shocked Nordic nation was gripped by reports that the gunman may not have acted alone.

The shooting spree began just hours after a massive explosion that ripped through an Oslo high-rise building housing the prime minister's office. At least 92 people have been killed, but police say more are missing.

The queen and the prime minister hugged when they arrived at the hotel where families are waiting to identify the bodies. Both king and queen shook hands with mourners, while the prime minister, his voice trembling, told reporters of the harrowing stories survivors had recounted to him.

A man who said he was carrying a knife was detained by police officers outside the hotel. He told reporters as he was led away that he was carrying the weapon because he didn't feel safe.

On the island of Utoya, panicked teens attending a Labour Party youth wing summer camp plunged into the water or played dead to avoid the assailant in the assault that may have lasted 30 minutes before a SWAT team arrived, police said. A picture sent out on Twitter showed a blurry figure in dark clothing pointing a gun into the water, with bodies all around him.

Buildings around the capital lowered their flags to half-staff on Saturday. People streamed to Oslo Cathedral to light candles and lay flowers; outside, mourners began building a makeshift altar from dug-up cobblestones. The Army patrolled the streets of the capital, a highly unusual sight for this normally placid country.

"This is beyond comprehension. It's a nightmare. It's a nightmare for those who have been killed, for their mothers and fathers, family and friends," Stoltenberg told reporters earlier Saturday.

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