The brother of a man gunned down by Anders Behring Breivik hurled a shoe at the mass killer, disrupting his trial in the Norwegian capital Oslo.
The outburst followed days of harrowing testimony from survivors of the massacre.
Police said the attacker was a brother of one of the 69 people Breivik shot dead on the small island of Utoeya last July during a youth camp organised by the ruling Labour Party.
The shoe missed Breivik but struck his co-defence lawyer, who was seated closest to the public gallery, during the presentation of an autopsy report.
The man was quickly escorted from court and police played down incident, saying it was a spontaneous emotional outburst rather than a dramatic breach of safety.
The Aftenposten newspaper named the man who threw the shoe as Hayder Mustafa Qasim, an Iraqi whose asylum seeker brother was killed on the island by Breivik.
Breivik admits the shootings and the killing of eight people in a bomb attack but denies criminal responsibility, saying he was defending Norwegian ethnic purity from Muslim immigration.
The incident evoked the gesture by an Iraqi reporter who hurled his shoes at former US President George W. Bush in 2008. Hitting someone with a shoe is considered particularly insulting in the Middle East because footwear is regarded as unclean.