Story highlights Oscar Pistorius' conduct was "negligent," Judge Thokozile Masipa says

She says Pistorius cannot be found guilty of intentionally killing his girlfriend

In addition to the murder charge, Pistorius faces three weapons charges

The most serious weapons charge is related to ammunition found in his house

Oscar Pistorius did not commit murder the night he killed Reeva Steenkamp, a judge said Thursday.

He did not intend to kill her, Judge Thokozile Masipa said.

But his conduct was "negligent," she said before adjourning for the day, suggesting she will find the Olympian guilty of culpable homicide.

There is no minimum sentence for culpable homicide in South African law. It's up to the judge to decide.

As he fired four bullets into the bathroom of his home in Pretoria on Valentine's Day last year, he did not foresee the "possibility that he would kill the person behind the door, let alone the deceased, as he thought she was in the bedroom at the time," Masipa said.

Evidence suggests that Pistorius genuinely believed the person in the bathroom was an intruder, although that is irrelevant to the case, the judge said.

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Pistorius could have taken other actions when he thought there was an intruder, she said. "All the accused had to do was to pick up his cell phone to call security or the police," she said.

"He could have run to the balcony and screamed in the same way he screamed after the incident," she added, noting that Pistorius called security after the incident and could have done so when he heard what he thought was an intruder.

Judge: Pistorius' background no excuse

Defense arguments that his upbringing "in a crime-riddled environment and in a home where the mother was paranoid and always carried a firearm" might explain his conduct that night, but "it does not excuse the conduct," Masipa said.

"The accused had reasonable time to reflect, to think and to conduct himself reasonably," she said. "I am not persuaded that a reasonable person with the accused's disabilities in the same circumstances would have fired four shots into that small toilet cubicle."

Following the country's legal standard for determining culpable homicide, Masipa found that "a reasonable person" would have "foreseen the reasonable possibility" that whoever was in the bathroom might have been killed, and would have "taken steps to guard against that possibility," she said.

"I am of the view that the accused acted too hastily and used excessive force," she said, adding that under the circumstances, "it is clear that his conduct was negligent."

Pistorius could be seen crying at times during the reading of the lengthy verdict.

The Olympian's trial in the death of his model and law graduate girlfriend started six months ago, transfixing the world with graphic details of how he fatally shot Steenkamp.

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Before she rejected the premeditated murder charge, Masipa questioned why he fired "not one ... but four shots" into the bathroom before he went to find his girlfriend.

However, she said, the intention to shoot does not necessarily mean the intent to kill.

Judge: Pistorius knew right from wrong

"Court is satisfied that at the relevant time, the accused could distinguish between right and wrong," and act accordingly, she said.

Masipa cast doubt on witness testimony and said she believes media coverage contaminated testimonies. She doubted state witnesses, saying they were in and out of sleep the night of the killing.

"Technology is more reliable than human perception and human memory," she said.

She described the victim's wound as "immediately incapacitating" and said she believed a scream heard by witnesses the night of the killing was Pistorius,' not Steenkamp's.

The judge appeared to be accepting the defense timeline of events that the shots came first, then screaming that must have been Pistorius.

She knocked down some aspects of the state's case: the fact that Steenkamp took her phone and locked herself in the bathroom allegedly out of fear for her safety, phone messages between the couple that showed some rocky patches, and her stomach contents.

Reeva Steenkamp was shot dead on February 14, 2013, by her Olympic sprint star boyfriend Oscar Pistorius.

Barry and June Steenkamp sat expressionless a few rows behind the man on trial for killing their daughter. Her father bowed his head as he heard about his daughter's fatal wounds.

Pistorius' uncle, sister and brother also attended the hearing in the packed courtroom -- the latter in a wheelchair from a car accident.

Lesser charges

Pistorius also faces three weapons charges.

The most serious relates to ammunition found in his house when police searched it after the killing. He did not have a proper license for it, but he says he was storing it in his safe for his father.

If he is found guilty of the ammunition charge, he could face up to 15 years in prison, though the judge could opt for a lesser punishment such as a fine or the loss of his gun license.

Oscar Pistorius cries during the verdict in his murder trial in Pretoria, South Africa.

Two other charges are related to allegations that he recklessly fired a gun in public -- once in a restaurant in 2012, and again out of the sunroof of a car last year. Pistorius denies both.

The maximum penalty for each charge is five years behind bars. If he is convicted of either, he could face a lesser sentence, such as a fine or the loss of his gun license.