“The security guard testified that he had shot and placed the object there himself,” Grete Lien Metlid from the Oslo Police told NRK at a press conference on Thursday morning.
The guard, who worked for the security firm Nokas, told police he had been shot at by two men, one of whom was white and spoke in English, at shortly before 3am in the morning.
He was treated in hospital for light injuries, as his chest was protected by a bullet proof vest.
But in his second police interview on Wednesday night, he broke down and confessed to what he had done.
The ‘attack' was the third incident involving the guard in the last three years, Metlid said. In 2013, he had several stitches in his arm after claiming to have been stabbed, and last November he was attacked with a stun gun and strangled by two assailants.
Metlid refused to comment on whether police believed the other two incidents had also been invented.
Police on Wednesday morning cordoned off the Blindern campus of Oslo University, restricted access to the local metro station, and instituted a no-fly zone after they found a "bomb-like object" close to the area where the man claimed to have been attacked.
By midday, the bomb disposal squad had ascertained that the object was a hoax.
The scare was magnified by tension in Norway surrounding the fourth anniversary of the attacks carried out by far-right extremist Anders Breivik on 22 July.
On Friday, the youth wing of Norway's Labour Party plans to hold it's first summer camp on the island of Utøya since the bloody massacre unleashed by the far-right extremist Anders Breivik in 2011.