Anders Behring Breivik distanced himself from friends in the years leading up to the deadly Norway attacks, according to testimony from childhood friends at his trial on Tuesday.
Four former friends gave evidence on the 26th day of Breivik's trial for the July attacks which killed 77 people, the BBC reported.
Breivik claims he shot dead 69 people on Utoeya island and killed another eight in a bombing in Oslo as part of a campaign against multiculturalism.
The witnesses explained he became "more serious, less social ... and lost the spark of life."
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The UK's Daily Telegraph reported others said Breivik was very concerned about his appearance: he got a nose job to appear more "Aryan," used makeup and was effeminate. Some suspected he was gay.
They testified he broke off all contact in 2006. At around the same time, he became reclusive, moved home to live with his mother and became "addicted to video games." He resumed contact with friends in 2011.
The BBC said the former friends have asked to remain anonymous and Breivik has been removed from the courtroom, watching proceedings from a nearby room. He admits carrying out the two attacks but denies criminal responsibility.
The trial is expected to end in late June. If found both guilty and sane, Breivik faces up to 21 years in prison.