Prosecutor Gerrie Nel made the allegation during final arguments in the sensational trial in a Pretoria courthouse, where the fathers of the Olympic runner and Steenkamp, a model and television personality, were in court for the first time since the trial began in early March. They sat at opposite ends of a long bench in the gallery.
Nel said a criminal trial was a "blunt instrument for digging up the truth'' but that he was confident of his case. He then said defense lawyers had argued that Pistorius acted in self-defense, fearing an intruder was in the house, but also raised the possibility that the once-celebrated athlete was not criminally responsible, accidentally shooting Steenkamp through a closed toilet door because he was "startled.''
"It's two defenses that you can never reconcile,'' Nel said.
The prosecution has argued that Pistorius intentionally shot Steenkamp before dawn on Feb. 14, 2013 after a quarrel. The defense has previously contended that he fired by mistake, thinking he was about to be attacked by an assailant in the toilet and that Steenkamp was in the bedroom.
In addition to the murder charge, Pistorius faces three separate gun-related charges, one of which stems from his alleged firing of a shot in a crowded restaurant called Tashas in Johannesburg, months before he killed Steenkamp. He has pleaded not guilty to all charges.
On Thursday, some of the state's written arguments as well as transcripts of past testimony appeared on screens in the courtroom. One section questioned Pistorius' defense case:
"Is it putative self-defense Is it an act of sane automatism Did he have criminal capacity to act Or was it all an accident as in Tashas Restaurant where he had the gun in his hand and it purportedly discharged itself''
Because South Africa has no trial by jury, Judge Thokozile Masipa will decide with the help of two legal assistants if Pistorius committed murder, is guilty of a negligent killing, or if he made a tragic error and should be acquitted. The runner faces 25 years to life in prison if convicted of premeditated murder, and also would be sent to prison for years if guilty of murder without premeditation or culpable homicide.
Earlier, Masipa told Nel and chief defense lawyer Barry Roux that they had only until the end of Friday to complete their final arguments in court.
"Unless, of course, you want to work on a Saturday and perhaps Sunday, after church,'' she said, smiling.