Steenkamp was shot dead in the early hours of Valentine's Day in 2013. Pistorius claiming he mistook her for a burglar when he fired four times through the door of his bedroom toilet.
"She [Reeva] was standing behind the door, she was not in a seated position," Mangena says.
"So, it could be that she ran into the toilet and she locked herself in the toilet, she was waiting, facing the door, inside the toilet.
"The first shot was on the hip and after this shot, she fell down. Most likely she could have screamed. She could have screamed and fell down."
Mangena used graphics to demonstrate the trajectory of the bullets in court, showing the standing position Reeva would have been in when the first shot was fired through the bathroom door and landed at her hip.
He then goes on to describe how he believes she fell into a seated position on top of a magazine rack - the location of which Pistorius knew - prompting him to change direction, firing three more shots, including the fatal wound to her head.
"He fired towards the position of the magazine rack. So, to me, it shows that he knew what he was doing," Mangena says.
During his trial Pistorius denied any suggestion that he knew Reeva was behind the door, often breaking down in tears weeping, wailing and praying whenever details of her injuries were heard.
But body language specialist Cliff Lansley claims on the Investigation Discovery show that this was a "useful tactic" used by the defendant and his legal team to curry favour with the judge.
