(CNN) -- Track star Oscar Pistorius was a "deceitful" witness who cannot escape a murder conviction for his actions, prosecutor Gerrie Nel said Thursday, presenting his closing arguments in the athlete's trial. On Valentine's Day last year, Pistorius shot dead his girlfriend, model and law graduate Reeva Steenkamp. This week, both prosecutors and defenders in Pretoria, South Africa, get their last chance to argue his culpability or innocence, after a trial lasting months that has gripped observers around the world. The state contends that Pistorius, 27, not only murdered Steenkamp, 29, but that it was premeditated. It's now up to Pistorius' defense team to argue for the last time before the judge that the athlete mistook Steenkamp for an intruder when he fired four shots through the locked toilet door, killing her.
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NEW: Defense attorney Barry Roux cites errors by the state as he starts his closing arguments
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Prosecutor argues Pistorius "cannot escape" a murder conviction as he wraps up state case
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Gerrie Nel labels Pistorius an "appalling" witness, says he was vague and argumentative
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The athlete's defense will make its closing arguments on Friday
Gerrie Nel
Gerrie Nel
For example, he cited multiple instances of @placeholder calling Pistorius a liar.
Gerrie Nel
Gerrie Nel
@placeholder told the court he had only found one example.
Barry Roux
And @placeholder reminded the court that Pistorius, who uses prostheses to walk after his lower legs were amputated as a child, suffers from anxiety.
Oscar Pistorius
Pistorius
Pistorius
Pistorius
Pistorius
Pistorius
Nicknamed "@placeholder" for the blade-like lower-leg prostheses he wears on the track, Pistorius has always admitted that he killed Steenkamp.