Prosecutor Gerrie Nel accused the former Olympic and Paralympic athlete of "adapting" his story to discredit physical evidence that the prosecution claims proves Pistorius could not have shot Steenkamp accidentally, believing that she was an intruder in his home on Valentine's Day last year.
Pistorius shot Steenkamp through a closed toilet door in a bathroom in his home. The prosecution says he intentionally killed her following an argument. Pistorius maintains he believed she was an intruder in his home.
Nel also accused Pisotrius of egotistical behaviour in his relationship, saying "your life is just about you."
Judge Thokozile Masipa is presiding over the trial. She 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.- INTERACTIVE | The state vs. Pistorius: how the accounts differ
- ANALYSIS | Oscar Pistorius under the microscope
Timeline: Oscar Pistorius