Judge Thokozile Masipa has ruled out murder charges for but could still find the Paralympian guilty of culpable homicide, or manslaughter.
The judge in the Oscar Pistorius trial has now ruled out all murder charges but could still find him guilty of culpable homicide, or manslaughter, for which he would face a long jail term, the BBC reports.
The Olympic double-amputee sprinter would have faced 25 years in jail if found guilty of premeditated murder at the court in Pretoria. He denies intentionally killing girlfriend Reeva Steenkamp on Valentine's Day last year, saying he thought there was an intruder.
Mr Pistorius 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 Thokozile Masipa said prosecutors had not proved he meant Ms Steenkamp, prompting tears from the Olympic sprinter.
But she said he acted hastily and had been negligent. Mr Pistorius, 27, says he thought an intruder was in the toilet.
The judge said a reasonable person would not have fired, the BBC reports.
"I am of the view that the accused acted too hastily, and used excessive force," she said.
"In the second census, it is clear that his conduct was negligent."
Judge Masipa had been speaking for several hours when she abruptly adjourned proceedings and said she would reconvene at 9.30am Friday local time.
She is expected to deliver a verdict of culpable homicide, or manslaughter, but has not yet spelled it out.
Earlier, Judge Masipa described Mr Pistorius as an evasive witness but said this did not mean he was guilty.
Clearing him of murder charges, she said he could not have foreseen killing whoever was behind the toilet door.
The South African Olympic and Paralympic sprinter had denied murdering Ms Steenkamp after a row on Valentine's Day last year, saying he shot her by mistake.
Judge Masipa has reviewed 4000 pages of evidence from the 41-day trial. During her summary, she questioned the reliability of several witnesses, saying humans were fallible and may not have heard gunshots or screaming as they thought, and there was "some doubt" that a woman screamed on 14 February.
She said the prosecution had failed to prove the Olympic athlete killed his girlfriend deliberately in the toilet after a row, prompting tears from Mr Pistorius.
But she then adjourned for lunch without ruling out culpable homicide, which suggests negligence without intention to kill.
Pistorius 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.
During his closing remarks last month, 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 world-wide attention.
Before the fatal shooting, Mr Pistorius was feted as a hero in South Africa and known as the "blade runner". He had won gold at the London 2012 Paralympic Games and also competed at the London Olympics.