Dressed in a dark suit, Pistorius, 27, responded methodically and in a soft monotone, and only occasionally did his voice rise. He did not break down in tears as he has previously this week in the witness box and did not look at Nel, instead facing the red-robed judge, Thokozile Masipa, on the dais.
The prosecutor seized on virtually every opportunity to challenge the star athlete's credibility, asserting that he had a string of unlikely excuses for why he wasn't to blame in the gun charges he faces on top of murder. In casting doubt on the Olympian's honesty, Nel was pushing the prosecution's argument that Pistorius is also lying that he killed Steenkamp by mistake, thinking she was an intruder, in the pre-dawn hours of Valentine's Day last year.
Nel briefly erupted in laughter after Pistorius suggested that two witnesses who said they once saw him shoot out of a car sunroof had collaborated and fabricated their accounts.
"I apologize for laughing, I won't do it again," Nel said after people in the gallery murmured in surprise at his outburst.
Masipa sternly cautioned him: "If you possibly think this is entertaining, it's not. So please restrain yourself."
The judge will deliver a verdict because there is no jury system in South Africa. Possibly because of her critical role, Masipa has given away little of her thinking during the trial, interjecting only occasionally during testimony and keeping an impassive expression.
In the cross-examination, Nel asserted that Pistorius will not "accept responsibility for anything." He reacted incredulously to the athlete's explanation of why a gun he was handling went off under a table in a packed restaurant. The incident, for which he was charged with firing a gun in public without good reason, happened weeks before Steenkamp died.
Pistorius said a friend's pistol, a Glock, went off while he was holding it but insisted that he hadn't pulled the trigger. But a police expert testified earlier at the trial that the Glock could not be fired without pulling the trigger.
"We have you in possession of the gun, a shot went off, but you didn't discharge the gun?" Nel said. "You are lying."
"I respect Mr. Nel's comment," Pistorius replied, "but I didn't pull the trigger on that firearm."
Pistorius said he wasn't guilty of another charge against him, illegal possession of ammunition for .38-caliber ammunition found in a safe in his home after he killed Steenkamp. He said they belonged to his estranged father, who had put the bullets in the safe. Nel retorted that Pistorius' father, Henke, had "refused" to make a statement to police on the ammunition being his.
At another point, Nel said caustically: "It's the strangest day today. You just don't take responsibility for anything."
Two contrasting images of Pistorius have emerged in court: the defense-led portrayal of a contrite man worried about crime who made a tragic mistake, and the prosecution's depiction of an overbearing egotist obsessed with firearms who killed his girlfriend on purpose after a heated argument.
Pistorius, who faces 25 years to life in prison if convicted of premeditated murder, said he did not intentionally fire the four shots that penetrated the toilet door. Steenkamp was struck in the head, hip and arm.
"I didn't have time to think about if I wanted to or didn't want to," Pistorius said when Nel asked whether he intended to shoot.
Nel also accused him of egotistical behavior in his relationship with Steenkamp, and described Pistorius' courtroom apology to her family on Monday as an insincere "spectacle."
"Your life is just about you," Nel told Pistorius. He said the athlete was not "humble enough" to apologize in private to the family and away from the media glare of a murder trial broadcast live around the world.
Pistorius said his lawyers had been in touch with representatives of Steenkamp's family, and that he believed they were not ready to meet with him.
"I completely understand where they're coming from," he said. "It's not that I haven't thought about them."
Nel also pressed Pistorius about Steenkamp's objection to his playing a song by American rapper Kendrick Lamar on a car stereo. Pistorius referred to the song in a cellphone message to Steenkamp that acknowledged her objections and has been included as evidence in the trial.
The prosecutor asked if the name of the song was "Bitch, Don't Kill My Vibe," but Pistorius said he couldn't remember the specific song. Nel responded that Steenkamp would have been right to take offense and caustically noted, "We can't ask her."