OSLO, Norway -- The Norwegian anti-Islam militant whose bomb attack and shooting massacre shocked this small country last summer was charged on Wednesday with terrorism and the premeditated murder of 77 people as officials prepared for a trial to start next month.

Prosecutors said they would initially seek a sentence of psychiatric care for the admitted killer but might demand 21 years in prison - Norway's nominal maximum - if an initial diagnosis of psychosis is contradicted by a second opinion.

Anders Behring Breivik, 33, has admitted carrying out a July bomb attack that killed eight people at government headquarters in Oslo and a gun massacre hours later that killed 69 people at a Labor Party summer camp.

Norway mass killer Breivik admits July massacre

His targets were "traitors" with immigrant-friendly attitudes, he explained at a preliminary court hearing.

"The defendant has committed highly serious crimes of a dimension we have no previous experience with in our society in modern times," prosecutor Svein Holden told reporters after unveiling the indictment.

He said the killings included "aggravating circumstances" but did not amount to crimes against humanity under Norwegian law.

A crimes-against-humanity charge would have carried a maximum 30-year sentence, but Holden told Reuters that Norway's law applies only to "widespread, systematic" atrocities and not the acts of an individual.

While the maximum conventional prison sentence for terror and murder in Norway is 21 years, courts are permitted after that to extend custody indefinitely if a violent, sane convict is considered likely to repeat his crimes.

Psychotic or sane?
Holden said the charge extends to the attempted murder of some 209 people injured in the bomb blast and 33 hurt in the summer-camp shooting on tiny but rugged Utoya Island.

Thirty-four of those killed at the island were under 17 years of age and the youngest was 14.

"Of the 69 who were killed, 67 were struck by lethal gunshots," prosecutor Inga Bejer Engh said in the first such public accounting. "Two died in falls or drowning without being shot."

The events of July 22 began several hours earlier when Breivik parked a Volkswagen van stuffed with 2,090 pounds of fertilizer and diesel fuel at the front entrance of Norway's prime minister office and set the fuse for seven minutes.

Breivik had already posted a 1,500-page compendium of anti-immigration writings on the Internet, claiming that European identity was under threat from waves of Muslim newcomers.

Court orders new mental review of Norway mass killer Anders Breivik

"In the defendant's own opinion these acts have been legitimate and lawful, and there is undoubtedly an obvious and evident fear that new serious offenses of the same nature may occur," the prosecutors said in the charge sheet.

A two-person psychiatric team has concluded Breivik was psychotic at the time of the attacks, and thus ineligible for prison. A second mental examination is under way, with a new report due six days before the April 16 start of the trial.

Breivik's lead attorney, Geir Lippestad, said the potential for conflicting psychiatric findings complicates the defense.

"We will have to prepare two lines (of defense) - both for sanity and insanity," he told broadcaster TV2 on Wednesday.

Under Norwegian law the trial will proceed without regard to Breivik's diagnosis until it is time for sentencing. If the judges agree he was psychotic during the attacks he can only be sentenced to psychiatric treatment, with periodic reviews.

More from msnbc.com and NBC News:

• One year after Fukushima, Japanese town is frozen in time
• Six British soldiers believed killed in Afghanistan
• Palestinian women allege abuses by Israeli security service
• Stranded kite surfer fends of shark for two days in Red Sea
• Syrian military hospitals torturing patients?
• High stakes for China iPad dispute

Follow us on Twitter: @msnbc_world