(CNN) -- Oscar Pistorius denied he picked on girlfriend Reeva Steenkamp, his murder trial heard Thursday, as the chief prosecutor sought to portray the track star as an arrogant hothead who is reckless with guns.
In a second day of blunt and aggressive questioning, prosecutor Gerrie Nel accused the double amputee of blaming other people for his mistakes, as he sought to prove the Olympic and Paralympic athlete murdered Steenkamp on Valentine's Day last year.
Nel began by picking apart message exchanges between the couple, accusing the runner of screaming at his girlfriend and acting selfishly toward her.
"I didn't treat her badly," Pistorius replied.
Asked if Steenkamp had lied when she said he picked on her incessantly, Pistorius replied: "She never lied."
He later added: "Reeva was never scared of me."
Nel highlighted an incident in which Steenkamp complained in a message that Pistorius asked her to stop chewing gum. He also read a message in which she defended herself against Pistorius' accusations that she flirted at a party.
"You were strong enough in that relationship to say stop your voices, stop your accents, stop chewing gum," Nel said. But Pistorius replied he gently told her to stop chewing gum before they got on camera at an event.
Nel said Pistorius never responded to Steenkamp's message in which she said, "I'm the girl who fell in love with you."
"We did a search ... the phrase 'I love you' appears twice on her phone, to her mother," the prosecutor said.
"Because it was all about Mr. Pistorius," Nel said. The athlete said he never got the opportunity to tell Steenkamp he loved her.
'You will blame anybody but yourself'
In his second day of cross-examination, Pistorius faced persistent questions about what happened on the night he shot Steenkamp. Nel said Pistorius' version of events on the night of the killing "is a lie" and accused him of "adapting" events to suit his account.
The runner recounted waking up during the night and getting out of bed to close the doors to a balcony, shut the curtains and move fans into the room. Steenkamp is then thought to have gotten out of bed, but the athlete said he was unable to see her because he had his back turned and the room was dark.
Pistorius insisted again that the shooting was an accident and he did not intentionally fire four shots.
Nel, with a reputation as one of South Africa's toughest attorneys, has sought to portray Pistorius as negligent with firearms.
"You will blame anybody but yourself," he said to the 27-year-old, cross-examining him about a separate incident in which Pistorius is accused of firing a pistol in a restaurant in January 2013.
Pistorius said the gun was given to him by a friend under a restaurant table and went off by itself as he tried "to make it safe." He had wanted to see the gun but conceded he hadn't checked the magazine first. Police Capt. Christian Mangena gave evidence earlier in the trial, saying the weapon could fire only if the trigger was pulled.
The athlete said he could not explain how the gun went off, and he questioned the decision of his own defense lawyer, Barry Roux, not to cross-examine Mangena on his evidence.
"Now you blame counsel Mr. Roux," Nel said.
Pistorius, the most composed he has been in days, said he repeatedly took the blame for the incident, but the prosecutor tried to poke holes in his declaration.
"This is incredible. You never touched the trigger, the gun went off. You took the blame, you took responsibility, but no one remembers," Nel said.
Pistorius also said two witnesses, an ex-girlfriend and a friend, were lying about an incident in which the runner is alleged to have fired his gun out the sunroof of a car. And he said he wasn't guilty of a fourth charge against him: illegal possession of ammunition found in a safe in his home after Steenkamp's death.
"You just don't want to accept responsibility for anything," Nel told Pistorius, whose answers to the accusations were short denials.
'You shot and killed her. Say it'
A day before, a defiant Nel bluntly barked at the Olympic star on the stand: "You shot and killed her. Say it -- 'I shot and killed Reeva Steenkamp,' "
No one disputes that Pistorius killed Steenkamp. But the prosecution is trying to prove beyond a reasonable doubt that he did so knowingly and intentionally.
The runner has admitted to the killing, but he said he mistook Steenkamp for an intruder in the bathroom when he fired through the door and killed her.
Before Nel went after Pistorius, Roux had tossed his client a question to drive that argument home. He asked Pistorius if he intentionally killed Steenkamp.
"I did not intend to kill Reeva or anybody else for that matter," he replied.
In a dramatic opening to his cross-examination Wednesday, Nel shocked the Pretoria court when he confronted Pistorius with a graphic photograph of Steenkamp showing the side and back of her skull, her hair matted with blood.
Pistorius broke down and sobbed as Nel pushed him repeatedly to take responsibility for her killing.
Pistorius has told the court what he remembered from the night Steenkamp died.
The prosecution alleges Pistorius killed his girlfriend after they argued.
Only those in the courtroom can see Pistorius because he has chosen not to testify on camera. His testimony can be heard on an audio feed.
'I'm obsessed with looking at him'
Earlier, the athlete said he would like to meet Steenkamp's parents to apologize.
"I don't think they will ever want to meet me," he said. "I am terribly sorry that I took the life of their daughter."
Steenkamp's mother, June, has sat in court throughout Pistorius' four days on the stand.
In an interview with the UK's Mirror newspaper, she said she was still trying to decide whether the sprinter was acting as he defended himself.
"I look at Oscar the whole time, to see how he is coping, how he is behaving. I'm obsessed with looking at him, it's just instinctive, I can't explain it," she said. "I keep thinking, 'let me see how he's taking this.' He has been very dramatic, the vomiting and crying."
Talking about Pistorius' apology this week, she said: "It left me unmoved. I knew it was coming. My lawyers had prepared me for it."
"I cried for the first time, 'Yes,' but not because he apologized, because of the suffering and agony that my darling daughter went through and because I will never have her again."
The trial is scheduled to continue until the middle of May. Judge Thokozile Masipa will decide the verdict in collaboration with two experts called assessors. South Africa does not have jury trials.
CNN's Richard Allen Greene, Brent Swails, Emily Smith and Faith Karimi contributed to this report.