Henke Pistorius reportedly added that his family had "zero doubt" the athlete had mistakenly shot Reeva Steenkamp thinking she was an intruder.
Pistorius' father told the newspaper: "When you are a sportsman, you act even more on instinct. It's instinct, things happen and that's what you do."
Pistorius will concentrate on defending himself against allegations that he murdered his model girlfriend on Valentine's morning.
The South African press say the weapon is a key piece of police evidence, but Pistorius' family said the death is a 'tragic accident.'
The family and management of Oscar Pistorius have released a statement disputing the murder charge against him 'in the strongest terms'.