The chief defense lawyer for Oscar Pistorius delivered final arguments in the athlete's murder trial on Friday, alleging that Pistorius thought he was in danger when he killed girlfriend Reeva Steenkamp and also that police mishandled evidence at the house where the shooting happened.

At one point, lawyer Barry Roux slapped his hand on the desk in front of him to mimic a sound that the double-amputee runner has said he heard on the night of Steenkamp's death. Such an alarming sound, Roux argued, explains why Pistorius thought an intruder was in his home and that he had to defend himself by opening fire.

On Thursday, chief prosecutor Gerrie Nel presented his final arguments that the athlete shot Steenkamp through the closed toilet door after an argument, describing him as an "appalling witness" who lied constantly during testimony to try to cover up the murder.

Roux said Pistorius' disability had made him particularly vulnerable and anxious over the years, comparing the runner to a victim of abuse who kills an abuser after a long period of suffering.

Pistorius has said he killed Steenkamp on Feb. 14, 2013 by mistake, thinking an intruder was in the toilet and about to attack him.

On Friday, Nel sat and listened as Roux alleged that items in Pistorius' bedroom, near the bathroom where he killed Steenkamp, may have been moved around by investigating officers.

"There was no respect for the scene," Roux said of the police investigation. He also noted that the former chief investigator, Hilton Botha, who later resigned from the force, was not called as a witness by the state.

The positioning of bedroom items, including a fan, a bedcover and a pair of Steenkamp's jeans, are important because, in police photographs, they were not in the places where Pistorius said they were before the shooting, leading prosecutors to argue that Pistorius is lying in his version of events.

The prosecution has argued that a fan was found standing directly in front of doors leading to the balcony, and therefore Pistorius' story that he ran to the doors, opened them and screamed for help after realizing he shot Steenkamp by mistake is not true. Prosecutors say Pistorius never went out to retrieve two fans before the shooting and move them inside, which the athlete says is the reason why he did not see Steenkamp get out of bed and go to the bathroom in the middle of the night.

The bedcover was shown crumpled on the floor in a police photograph. Pistorius had claimed it was on the bed, leading him to believe Steenkamp was underneath it in the bed when he went to the bathroom with his gun.

The premeditated murder charge carries a sentence of at least 25 years to life in prison. Pistorius could also be convicted of a lesser murder charge or negligent killing, both of which call for years in jail. Judge Thokozile Masipa could acquit him if she believes he only made a tragic error.

Masipa was expected to adjourn the trial at the end of proceedings Friday to deliberate on a verdict with the help of two legal assistants. South Africa does not have a jury system.