The 27-year-old Paralympian wrapped up three days of emotional and harrowing defence testimony by denying he wanted to kill girlfriend Reeva Steenkamp or the intruder he believed to be behind a toilet door in his home on the night of Valentine's Day last year.
"I did not intend to kill Reeva, milady, or anyone else," he told the murder trial, in his strongest rebuttal yet of charges against him.
Pistorius claims he mistook Steenkamp for an intruder.
But he could also face a murder charge if the prosecution shows he intended to kill when his life was not threatened -- regardless of whether he knew who was behind the door.
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After Pistorius's denial, prosecution lawyer Gerrie Nel began a searing cross-examination, immediately confronting Pistorius with the magnitude of his actions on February 14, 2013.
After Pistorius conceded he made a terrible "mistake", Nel -- nicknamed "the bulldog" for his tenacious courtroom performance -- was incredulous.
"You made a mistake? You killed a person, that's what you did!" he thundered.
Pistorius's cross-examination is expected to be a key point in his trial, a stern test of both his version of events and of his resolve.
During five weeks of proceedings the world-famous athlete has appeared fragile, frequently crying in court and becoming physically sick when the gruesome details of Steenkamp's injuries were discussed.
He is likely to remain on the stand for the remainder of this week as his extensive testimony probed and picked at by Nel, who once successfully prosecuted a South African police commissioner.