The prosecution in Oscar Pistorius’s murder trial in Pretoria accused him today of tailoring his testimony and using his emotional state to hide frustration at an “improbable” version of events from the night his girlfriend, Reeva Steenkamp, was killed.

Pistorius broke down several times during his testimony. The star runner stood by his story that the Feb. 14, 2013, shooting was accidental, but said “I blame myself for taking Reeva’s life.”

Gerrie Nel, chief prosecutor, opened the fourth day of cross-examination by alleging that Pistorius had "concocted" his account of the shooting. 

"You're tailoring your version as you're sitting there," Nel said. Later, he accused Pistorius of being a stickler for detail on some matters, in contrast to his frequent statements on the witness stand that he could not remember aspects of his testimony.

Pistorius stood by his defence that he thought there was an intruder in the house. After a long pause after the question, he said he screamed, using an expletive, for the purported intruder to get out of his house. 

"I was terrified," Pistorius said when asked about the moments before the shooting. 

As he testified, Pistorius began to wail and Judge Thokozile Masipa called an adjournment. 

Nel — who has been nicknamed "pitbull" by local media — resumed attacking Pistorius's account of the shooting after the adjournment.

Nel asked Pistorius about how he approached the door and how he held his gun. Pistorius said in the moments before he fired, he was leaning against the wall, trying to keep his balance on the slippery floor. He held the gun out in front of him, but Pistorius refused to say he was aiming the gun.

“I was trying to stay put, so I could make sense of the situation,” Pistorius said.

He said he fired when the door appeared to move and he thought someone was going to come out and attack him.

“I didn’t have time to think,” Pistorius said.

Nel argued forcefully against that notion, claiming Pistorius was thinking as he approached the door. Nel said Pistorius knew who he was firing at.

“It’s not true,” Pistorius wimpered.

“Why are you getting emotional now?” Nel said, launching into his version of events again before being cut off by Pistorius.

“I did not fire at Reeva,” Pistorius said, his voice raising into a wail.

Nel moved for court to adjourn immediately after that, as Pistorius was too emotional to continue with questioning. 

During a final session of questioning, Nel attacked Pistorius's actions after the athlete fired four shots into the toilet door. Pistorius said his ears were ringing from the gunfire as he went back into the bedroom to look for Steenkamp. When he didn't find her on the bed, or hiding behind curtains, Pistorius said he immediately feared she was in the toilet.

Nel called that "improbable," and asked Pistorius repeatedly why he didn't think Steenkamp could have fled from the bedroom altogether. Checking the bathroom when there could have still been an intruder in there, Nel argued, wasn't normal.

"Nothing was normal about that night," Pistorius responded.

Pistorius began crying again as he described approaching the toilet for a second time, his gun still cocked, with the concern Steenkamp was inside.

“Why are you getting emotional now?” Nel asked.

"You’re getting frustrated because your version is improbable ... you’re not using your emotional state as an escape, are you Mr. Pistorius?”

Monday is Pistorius's fourth day being cross-examined by Nel, who has questioned the athlete about his ego and accused him of "adapting" his story.

Pistorius is the defence's second witness. The defence is expected to call more than a dozen witnesses.

Masipa alone will determine Pistorius's fate as South Africa does not have trial by jury.

If convicted of premeditated murder, Pistorius faces 25 years to life in prison.

Timeline: Oscar Pistorius

With files from The Associated Press