The judge, Thokozile Matilda Masipa, also found that, while Mr. Pistorius acted "unlawfully," he could not be found guilty of a lesser form of murder in the killing of his girlfriend, Reeva Steenkamp, 29, whom he shot and killed in the early hours of Valentine's Day, Feb. 14, 2013, in the mistaken belief, he has said, that she was a burglar at his home.
Sitting in a wooden dock in a dark suit, white shirt and black tie, 27-year-old Pistorius slumped forward and sobbed as the judge spoke.
But her ruling did not amount to an acquittal. Shortly before she adjourned the hearing for lunch, she said there was also the charge of culpable homicide to consider - the least serious offense, which offers the judge wide discretion in sentencing.
Premeditated murder, by contrast, carries a minimum 25-year term.
The judge's findings were delivered in a cool and clinical appraisal of a case that has riveted South Africa, been broadcast around the globe and has been compared to the O.J. Simpson case in the United States. Her judgment seemed a huge setback for the prosecutor, Gerrie Nel, who had called for Mr. Pistorius to be convicted of murder and whose pugnacious courtroom manner earned him the nickname "Pitbull."
In his version of the shooting, Mr. Pistorius, has said he awoke from his bed and heard what sounded like a window opening in the bathroom, making him think that an intruder had entered his home.
Then, walking on the stumps of his legs in a darkened passageway, with a handgun thrust out before him, he opened fire on a locked toilet door. Only later, he testified, did he suspect that Ms. Steenkamp was inside. When he broke down the door with a cricket bat, he said, he discovered her bloodstained body.
"Before I knew it, I had fired four shots at the door," Judge Masipa quoted Mr. Pistorius as saying, as she listed the various ways he described the shooting during the trial. At times, he said he shot "in the belief that the intruders were coming out" to attack him. At other moments, he said "he never intended to shoot anyone" and had not fired purposefully at the door, the judge said. Part of Mr. Pistorius’s evidence, she said, was "inconsistent with someone who shot without thinking."
Ms. Steenkamp, Judge Masipa added, "was killed under very peculiar circumstances," but "what is not conjecture is that the accused armed himself with a loaded firearm."
Nonetheless, the judge ruled, the prosecution's evidence to support a charge of premeditated murder was "purely circumstantial."
"The state clearly has not proved beyond reasonable doubt that the accused is guilty of premeditated murder,” she said. “There are not enough facts."
Much of the trial, in 41 days of testimony since it opened in March, has revolved around Mr. Pistorius's state of mind and intentions when he opened fire. During cross-examination in April, Mr. Pistorius sobbed, wailed and retched as he recalled the events surrounding Ms. Steenkamp's death.
While she accepted that Mr. Pistorius "would feel vulnerable" because of his disability," the judge said, he had been "a very poor witness" and had been evasive and "lost his composure" under cross-examination.
Until the killing, Mr. Pistorius, who had challenged able-bodied runners only months earlier at the London Olympics in 2012, seemed to be reveling in a glittery career of sporting success and celebrity acclaim.
The athlete, Judge Masipa said, had denied the state’s accusation that he killed Ms. Steenkamp after an argument, and had denied that he acted with premeditation. She said it was "common cause" that, after the shooting, Mr. Pistorius broke down the locked toilet cubicle door, cried out for help and was in an emotional state.
Judge Masipa said the issues were limited to whether Mr. Pistorius "had the requisite intention" to commit murder and "whether there was any premeditation."
"There were no eyewitnesses," Judge Masipa said, and the only people at the scene when the shooting happened were Mr. Pistorius and Ms. Steenkamp.
As the trial unfolded, the defense and the prosecution offered Jekyll-and-Hyde depictions of Mr. Pistorius's character.
The prosecutor, Mr. Nel, described him as trigger-happy, mendacious, narcissistic and prone to rage. By contrast, the lead defense lawyer, Barry Roux, sought to present him as anxious, vulnerable and fearful of South Africa's violent crime, laboring under the psychological burden of growing up since the age of 11 months with both legs amputated below the knee.
In part, the trial has been held up as evidence of a dramatic reversal of South Africa's white-dominated apartheid-era legal system. In 1998, four years after South Africa's first democratic election, Judge Masipa, who is 66 today, became only the second black female judge to be appointed to the High Court. Born in a poor township, she had been a social worker and newspaper journalist before studying law at the height of the apartheid era. Now, under South African judicial protocols, lawyers and witnesses are obliged to address her with the honorific "My Lady."
But the trial has also highlighted the country's continued racial preoccupations and its high levels of crime against women. In other cases, Ms. Masipa has handed down tough sentences in cases of rape and violence against women.
Judge Masipa dismissed two elements in the prosecution case relating to the state of Mr. Pistorius's relationship with Ms. Steenkamp as revealed in text messages and to suggestions that she had eaten far later in the evening than the runner had maintained. "None of this evidence proves anything," she said of the text messages which, the prosecution said, revealed that the runner’s relationship with Ms. Steenkamp was broken.
"Normal relationships are dynamic," Judge Masipa said. "Human beings are fickle."
Oscar Pistorius also faces three counts relating to firearms offenses.
[- Agencies]