A security guard says Oscar Pistorius initially told him "everything is fine" after neighbors in the athlete's gated community heard him shooting his girlfriend.
Pieter Baba testified Friday, the fifth day of Pistorius' trial in Pretoria, South Africa.
Baba said he and another guard drove to the athlete's house and called him after neighbors reported the shots. He said Pistorius assured him at first, but then broke down crying.
He said Pistorius called him back, crying without saying a word before the line was cut off.
Pistorius has admitted to shooting girlfriend Reeva Steenkamp, but says he mistakenly believed he was firing at an intruder.
Video report by Anita Powell from Pretoria
Prosecutors say Pistorius killed Steenkamp after an argument.
The testimony from one of the first responders capped a week of dramatic developments at the Pistorius trial.
Earlier, one of the witnesses, a neighbor, said she heard a a woman screaming before shots were fired at Pistorius's home on February 14, 2013.
The defense has asserted that witnesses heard Pistorius, not Steenkamp, screaming that night.
However, Pistorius' ex-girlfriend, Samantha Taylor, testified on Friday that Pistorius screams like a man.
She also testified that he kept a gun on him "all the time". On one occasion she said he fired it out of anger after police pulled him over while they were dating.
On Thursday, radiologist Johan Stipp testified he entered the athlete's home minutes after the shots and found the Olympic athlete kneeling and praying over the 29-year-old model.
Stipp says Pistorius was "emotionally very, very upset," adding that he thought the athlete was going to hurt himself.
Pistorius has pleaded not guilty to charges of murder, recklessly discharging a firearm and illegally possessing ammunition.
If convicted of premeditated murder he faces a life sentence.
Pistorius is known as the "Blade Runner" for his carbon-fiber prosthetic legs. In 2012, he became the first double-amputee to compete in the Olympics.