Norway's national news agency says police are investigating whether a second suspect was involved in a shooting spree on an island where 85 people were killed.
Police have arrested one man on preliminary charges in the massacre and a bombing in Oslo hours earlier.
NTB is reporting that witnesses told police two people were involved in the shooting on Utoya island. The agency says police are looking into it.
The agency says that the second man apparently wasn't disguised in police uniform. The man under arrest was wearing a sweater with a police emblem on it.
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In total, 91 people were killed in the two attacks.