A forensics expert has staged a re-enactment of how Paralympian and Olympian Oscar Pistorius broke down the door of the toilet where he shot dead his girlfriend.

Police Colonel Gerhard Vermeulen brought two pieces of physical evidence, a door and a cricket bat before the court.

In opening testimony, Col Vermeulen demonstrated how the door was struck with the bat, which was in turn used to wedge open a gap between a panel and the inner frame.

"The bat went through the door and there are actually marks on the tip of the bat which correspond with what happened," he said. 

"The person kind of twisted the bat to break open the door."

The sequencing of gun shots and the damage caused by the bat is crucial to both prosecution and defence account of events on 14 February, 2013.

The athlete says he mistakenly shot his girlfriend Reeva Steenkamp through the locked dark door four times, believing she was an intruder, but after realising his mistake broke it down with a cricket bat.

The prosecution says Mr Pistorius first hit the door with a bat in an effort to get to Ms Steenkamp, and then shot through the door.

Col Vermeulen demonstrated that height measurements showed Mr Pistorius was not wearing his prostheses at the time he struck the door.

Mr Pistorius claims he had his prostheses at the time, having put them on in an attempt to first kick the door down.

During eight days of testimony, the prosecution has already called upon witnesses who have testified hearing arguing, screaming and gunshots coming from Mr Pistorius's house.

A pathologist who conducted Ms Steenkamp's post-mortem report has also testified, but did not detail the exact sequence of events on the night.

He testified that Mr Pistorius shot Ms Steenkamp, a 29-year-old model and law graduate, with "Black Talon" ammunition, which mushroom open like a jagged flower on contact to cause maximum tissue damage.

Earlier today, Mr Pistorius's defence lawyer Barry Roux accused one of the runner's former friends who painted Mr Pistorius as reckless, disdainful of authority and with a passion for guns, as "engineering false evidence".