Geologist and former police forensic analyst, Roger Dixon, said the weight of the bullet casing did not add up.
He testified for the defence that the Black Talon bullet which hit Steenkamp weighed around 127 grains.
The one found in the toilet weighed 65.9 grains. One grain is about 0.06 grams. Dixon explained that adding this to that of the projectile found in Steenkamp’s skull, the numbers did not add up, meaning it could not have been the same bullet.
He agreed with the testimony of a police official who earlier told the court that the first shot Pistorius fired probably struck Steenkamp’s hip.
As Dixon spoke about the wounds on Steenkamp’s body, Pistorius leaned forward and held his head in his hands. His sister, Aimee, who sat in the court gallery, was also visibly upset.
Pistorius is on trial for the murder of Steenkamp. He shot her dead through the locked toilet door of his home on Valentine’s Day last year, apparently thinking she was an intruder.
The State argues Pistorius intentionally shot her following an argument. He 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 the charges.