The judge in the Oscar Pistorius trial has questioned the reliability of several witnesses in court, as she delivers her verdict on the athlete.
Judge Thokosile Masipa said humans were fallible, and may not have heard gunshots or screaming as they thought.
Correspondents say this could make a premeditated murder verdict unlikely.
The South African Olympic sprinter denies murdering Ms Steenkamp on Valentine’s Day last year, saying he thought there was an intruder.
The judge could also find him guilty of culpable homicide, or manslaughter, for which he would face a long jail term.
Mr Pistorius, 27, has pleaded not guilty to all the charges he faces, including two counts of shooting a firearm in public and the illegal possession of ammunition.
Judge Thokosile Masipa began by detailing the charges against the athlete and repeating extracts of his testimony, reading in a slow, measured way.
She then moved on to a summary of the trial.
A tense-looking Mr Pistorius looked on from the dock, and then began to weep.
Judge Masipa said that defence claims that police contaminated evidence and removed items from the crime scene “paled into insignificance”.
But she questioned the reliability of several witnesses who apparently heard screams and gunshots at the time of the incident, saying most of those who said they had heard the incident had “got facts wrong”.
The judge also said that the court would not make inferences about the state of the relationship between Mr Pistorius and Ms Steenkamp. The prosecution has suggested that it was “on the rocks”.
The BBC’s Andrew Harding says the court is witnessing Judge Masipa’s logic and style – gentle, tolerant of error from witnesses, but razor sharp.
And he says that her conclusion that the state had not contradicted Mr Pistorius’s version – that it was he who had screamed – suggests that a premeditated murder verdict is unlikely.
Correspondents say the judge appeared to be moving much more quickly than expected through the evidence, in a process which had been expected take hours or even days.
During his closing remarks last month, his lawyer Barry Roux conceded that the athlete should be found guilty of negligence for discharging a firearm in a restaurant – which carries a maximum penalty of five years.
Most of the trial, which began on 3 March 2014, has been televised and attracted worldwide attention.
Before the fatal shooting, the 27-year-old athlete was feted in South Africa and known as the “blade runner”.
He had won gold at the London 2012 Paralympic Games and also competed at the Olympics.
The judgement at his trial is likely to be well over 100 pages. The judge is going through each charge, summing up the prosecution and defence cases and analysing the evidence.
Ms Steenkamp, a 29-year-old model and law graduate, was hit three times by bullets shot through a toilet door by Mr Pistorius at his home in the capital, Pretoria, in the early hours of 14 February 2013.
He denies the prosecution’s allegation that the couple – who had been dating for three months – had rowed.
The athlete said he thought she was still in the bedroom when he heard a noise in the bathroom, which he believed to be an intruder.
The prosecution have tried to characterise Mr Pistorius as a “hothead”, while his defence team have portrayed him as having a heightened response to perceived danger because of his disability and background.
In July, a psychiatric report requested by the judge said Mr Pistorius had post-traumatic stress disorder but no mental illness that could prevent him being held criminally responsible for his actions.