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(CNN) -- Oscar Pistorius faced another day of relentless cross-examination Friday as the prosecution sought to pick holes into his account in the killing of his girlfriend, Reeva Steenkamp.
Prosecutor Gerrie Nel has accused the athlete of hiding the truth about the death of Steenkamp, whom he shot last year through a closed toilet door in his home.
A day earlier, the athlete denied he acted selfishly toward her as Nel sought to portray him as an arrogant hothead who is reckless with guns.
In a bid to paint their relationship as rocky, he ripped apart message exchanges between the couple Thursday.
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.
'I'm the girl who fell in love with you'
The prosecution challenged almost every aspect of the athlete's credibility, including accusing him of lying that he killed his girlfriend by mistake on Valentine's Day last year.
Nel sought to paint him as selfish, and demanded to know why the athlete did not respond to his girlfriend's declaration of love.
"We did a search ... the phrase 'I love you' appears twice on her phone, to her mother," the prosecutor said.
Pistorius, he said, never responded to Steenkamp's message in which she said, "I'm the girl who fell in love with you."
But Pistorius said he preferred to talk to his girlfriend over the phone rather than messaging. He acknowledged he never got a chance to tell her that he loved her.
"Because it was all about Mr. Pistorius," Nel said.
"You just don't want to accept responsibility'
In his second day of cross-examination Thursday, 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 may have gotten out of bed at that point, but the athlete said he didn't see her because he had his back turned and the room was dark.
Nel sought to portray Pistorius as negligent with firearms in relation to a separate incident in which he fired 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."
The athlete could not explain how the gun went off, and said he repeatedly took the blame for the incident.
"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 said.
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 said he mistook Steenkamp for an intruder in the bathroom when he fired through the door and killed her.
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.
He broke down and sobbed as Nel pushed him repeatedly to take responsibility for her killing.
The prosecution alleges Pistorius killed his girlfriend after they argued. Several witnesses have testified to hearing a man's shouts coming from the house, although they have also spoken of the terrified screams of a woman leading up to and during a volley of shots.
The trial has gripped South Africa, where Pistorius is considered a symbol of triumph over physical adversity. His disabled lower legs were amputated when he was a baby, but he went on to achieve global fame as the "Blade Runner," winning numerous Paralympic gold medals on the steel blades fitted to his prostheses.
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'
The athlete said Thursday 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 this week.
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."
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.
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