The chief prosecutor, Gerrie Nel, continued cross-examining the former Olympic and Paralympic runner, who is accused of premeditated murder.
Pistorius claims he shot his girlfriend, Reeva Steenkamp, accidentally, believing she was an intruder locked in the toilet of a bathroom in his home.
The prosecution has argued he fatally shot her following an argument on Valentine's Day last year.
On Wednesday, Nel urged the athlete to "take responsibility" for fatally shooting Steenkamp and urged him to look at a graphic police photograph of her bloodied head.
Pistorius refused to look at the photo, saying he can remember it.
"I will not look at a picture where I'm tormented by what I saw and felt that night ... I remember. I don't have to look at a picture. I was there."
Judge Thokozile Masipa is presiding over the trial. She alone will determine Pistorius's fate as South Africa does not have trial by jury.
Pistorius faces 25 years to life in prison if convicted of premeditated murder.- ANALYSIS | Oscar Pistorius under the microscope
- DIAGRAM | State vs. Pistorius: How the accounts differ
Timeline: Oscar Pistorius