Pistorius denied the allegation that he said to the close friend of the girlfriend he killed: "How can you sleep at night?"
The accusation by Kim Myers provided a bizarre twist during the trial of the world-famous double-amputee Olympian, who is facing 25 years to life in prison if convicted of premeditated murder for shooting Steenkamp, a 29-year-old model, at his home last year.
Pistorius, 27, says he killed her by mistake, thinking she was an intruder when he shot her multiple times through a closed toilet door.
He also denied to reporters in the courtroom that he made any comment to Myers. Pistorius said he hasn't spoken to members of the Myers family for weeks, despite sitting a few feet away from them during court proceedings.
Myers was approached by Pistorius and he made the remark to her in a "very sinister way," the lawyer for Myers told The Associated Press. Attorney Ian Levitt said Myers was "shocked" and did not know what it referred to. Levitt said she found it "extremely disturbing."
"It's important to confirm this. It was in front of witnesses. Journalists have witnessed this," Levitt said of the alleged comment. Levitt was not in the courtroom but said Myers phoned him to report it.
Reporters said Pistorius apparently made a comment to Myers as he walked close to the court benches reserved for family and friends of both Pistorius and Steenkamp. Levitt added that he made a complaint to state prosecution officials, although officials at South Africa's National Prosecuting Authority said they would not take action.
The Myers family was very close to Steenkamp, who lived with them after moving to Johannesburg to further her modeling career. They referred to themselves as her second family and have attended much of the trial.
One of Pistorius' lawyers, Brian Webber, said Pistorius told him that Myers' allegation was untrue.
"I've asked the client and he denies that he said it," Webber said.
During trial proceedings, two women who lived on either side of the house where Pistorius killed Steenkamp were called by the defense as witnesses and were asked to make high-pitched wails while testifying. The defense was trying to show that Pistorius' cries on the night of the shooting could be confused with a woman's screams.
The prosecution maintains that Pistorius killed Steenkamp intentionally and after she screamed during a loud fight. Other neighbors testified that they heard a woman screaming before and during the sound of gunshots -- evidence of a heated argument between the couple, according to prosecutors.
The defense says only Pistorius screamed, first to warn off a perceived intruder and then in desperate panic after realizing he had shot Steenkamp by mistake through the stall door in his darkened bathroom. In total, three next-door neighbors were summoned by the Olympian's defense on the 27th day of testimony. They all testified that they heard a man's high-pitched cries but not a woman screaming.
The neighbors were briefly cross-examined by chief prosecutor Gerrie Nel, who sought to show that they had heard events after the fatal shooting and their testimonies were irrelevant to a possible fight between the couple.
During testimony, Pistorius sat on his wooden bench looking impassively at times at the witnesses, who all described him as friendly and a good neighbor. His legal team says it could wrap up presenting his defense by next Tuesday.