Prosecutor Gerrie Nel warned that South Africans might lose trust in the courts and take the law into their own hands if Pistorius is punished too lightly for the death of model Steenkamp.
Pistorius shot the 29-year-old four times through a locked bathroom door on Valentine's Day last year. He claims he thought she was an intruder who had broken into his Pretoria home, The Mirror reported.
Nel dismissed a recommendation to put Pistorius under house arrest and be given community service as shockingly inappropriate. He challenged probation officer Annette Vergeer, who warned prison would put Pistorius in danger, telling her that society demands that if one kills a person, there should be a harsh punishment.
Pretoria high court judge Thokozile Masipa will decide the sprinter's fate at the end of the weeklong sentencing hearing, the report added.