PRETORIA, South Africa -- The judge in Oscar Pistorius' trial ruled out a murder conviction for the double-amputee Olympian on Thursday in the shooting death of his girlfriend but said he was negligent, raising the possibility he will be convicted of culpable homicide.

The verdict in the case that has riveted much of South Africa and the world is expected Friday when Judge Thokozile Masipa reconvenes the judgment phase, climaxing the trial that began in March.

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Even if Pistorius is acquitted of murder, he could still be sent to jail for a maximum of 15 years if convicted of culpable homicide, which is the killing of someone through reckless or negligent behavior, although five years in prison is a guideline when a firearm is used.

The red-robed Masipa, sitting in the dais and looking down at Pistorius and the packed courtroom, said she felt Pistorius acted negligently when he fired four times through a toilet door in his home in the predawn hours of Valentine's Day last year. In a moment of high drama, Masipa stopped reading out her verdict in the six-month trial and adjourned until Friday.

Because there is no trial by jury in South Africa, Masipa is expected to explain exactly why she and her two legal aides came to the decision they have before the judge issues the verdict.

"I am of the view that the accused acted too hastily and with excessive force," Masipa said of Pistorius' actions on the fatal night.

She said the prosecution had not proved beyond a reasonable doubt that Pistorius committed premeditated murder. She also ruled out a lesser murder charge. As she indicated that Pistorius would likely be cleared of murder, he began sobbing quietly on the wooden bench, his shoulders shaking.

Murder is an illegal, intentional killing. A premeditated, or planned, murder would carry a heavier sentence in the event of a conviction.

The world-famous athlete has acknowledged firing the shots that hit Reeva Steenkamp in the head, arm and hip area with hollow-point bullets from his 9 mm pistol. He said he mistook her for an intruder and denied murdering her, but the judge said Pistorius still could have taken other action, like calling the police or security at his housing estate.

Oscar Pistorius has said he killed girlfriend Reeva Steenkamp by mistake last year, fearing that there was an intruder in his home. Gianluigi Guercia/AFP/Getty Images

"Did the accused fail to take steps he should have taken? Yes," Masipa said. "He failed to take any steps to avoid the death."

The prosecution alleged that the athlete intentionally killed his girlfriend, a model and budding reality TV star, after a loud nighttime argument heard by neighbors. Masipa said there were "just not enough facts" to support the finding of premeditated murder or the lesser murder without planning.

"The accused cannot be found guilty of murder," the judge said.

At the start of the judgment hearing, Masipa told Pistorius, 27, that he should remain seated on the bench while she read her findings out and until she asked him to stand for the verdict.

In her hours-long assessment of witness evidence, she called Pistorius a "very poor witness" who had lost his composure on the stand and was at times "evasive." But Masipa emphasized that did not mean he was guilty of murder.

The 66-year-old judge also cast doubt on witness accounts of hearing a woman's screams, a key part of the prosecution's case. The defense had argued that it was Pistorius who was screaming in a high-pitched voice after discovering he had fatally shot Steenkamp.

Masipa cited testimony of an acoustics expert called by the defense, saying it cast serious doubt on whether witnesses who were hundreds of meters away in their homes -- as some state witnesses were -- could have differentiated between the screams of a man or a woman.

At one point, Masipa said: "I continue to explain why most witnesses got their facts wrong."

Masipa said she was disregarding text messages between Steenkamp and Pistorius that had been entered as evidence. Prosecutors had submitted text messages that showed tension between the couple while the defense submitted messages that indicated mutual affection. That evidence, the judge said, doesn't prove anything.

"Normal relationships are dynamic and unpredictable most of the time, while human beings are fickle," she said.

Pistorius faced 25 years to life in prison if convicted of premeditated murder. He faced a minimum of 15 years if found guilty of murder without planning.

He was charged with murder, two counts of unlawfully firing a gun in a public place in unrelated incidents and one count of illegal possession of ammunition.

Before Thursday's session began, Pistorius hugged his brother Carl, who was seated in a wheelchair because of leg injuries suffered in a recent car crash. The parents of Steenkamp were also in the packed gallery. Other members of Pistorius' family, including his father, Henke, sat behind him.

If Pistorius is convicted on any charge, the case will be postponed until a later sentencing hearing.