Oscar Pistorius sits in the dock during his murder trial in the North Gauteng High Court in Pretoria on May 8, 2014. Picture: Gianluigi Guercia

Johannesburg -

Ballistics expert Thomas “Wollie” Wolmarans is expected to return to the stand in Oscar Pistorius's murder trial at the North Gauteng High Court in Pretoria on Friday.

The defence team called Wolmarans on Thursday.

Pistorius maintains that he thought his girlfriend, Reeva Steenkamp, was an intruder when he shot her in his Pretoria home on February 14 last year. He has been charged with murdering her.

He shot through the locked door of his toilet, hitting Steenkamp in the hip, arm and head. He apparently thought she was an intruder about to open the door and attack him.

Wolmarans said he found a fragment of a bullet in Pistorius's toilet bowl, missed by investigators who had already searched the crime scene, and handed it to police.

He said an accurate determination of the sequence of the shots or Steenkamp's body position when she was shot was not possible.

Pistorius is also charged with three contraventions of the Firearms Control Act - one of illegal possession of ammunition and two of discharging a firearm in public.

He has denied guilt on all four charges. - Sapa