Pistorius, 27, is charged with premeditated murder in Steenkamp's shooting death on Feb. 14 last year and faces 25 years to life in prison if convicted. He says he shot Steenkamp, 29, by mistake through a locked door in his bathroom because he thought she was a dangerous nighttime intruder.
Pistorius says Steenkamp went to use the toilet during the night without him knowing, but prosecutors charge he killed her after a loud argument that caused her to flee and hide in the toilet area. Neighbors have testified to hearing loud screaming before and during the shots being fired.
Mangena, the ballistics expert, concluded that one of the final two bullets fired by Pistorius went through Steenkamp's left hand, which she held over her head, before it penetrated her skull. The policeman said he couldn't determine the order of the last two shots.
As Mangena threw his hands up to cover his head in court to re-enact Steenkamp's cowering position, and described details of the head wound, Pistorius put his fingers in his ears in an apparent attempt to block out the testimony.
June Steenkamp, Reeva's mother, was in the courtroom and occasionally glanced at photos of the bloody scene of her daughter's shooting.
Mangena said the bullet that struck Steenkamp's skull broke into two fragments, one of which exited her head and struck the wall behind her. The first shot into the right hip broke Steenkamp's hip bone, Mangena said.
"I'm of the opinion that after this wound was inflicted, my lady, she dropped immediately," Mangena said, addressing the judge. Steenkamp slumped into a "seated or semi-seated position" on top of the magazine rack in the cubicle, where she was hit another two times, he said.
Pistorius fired from a distance of at least 60 centimeters (24 inches) and no further than 3 meters (9.8 feet) away, where there was a wall behind him, Mangena said. He described the impact of the hollow point bullets in Pistorius' gun, which were designed to cause maximum damage to an intended target.
"It hits the target, it opens up, it creates six talons, and these talons are sharp," Mangena said. "It cuts through the organs of a human being."
The defense said it would challenge Mangena's testimony regarding the sequence of the shots.
Also Wednesday, the chief prosecutor said he planned to wrap up his case early next week after calling four or five more witnesses. Judge Thokozile Masipa granted Nel's request to adjourn the trial until Monday so that Nel has time to consult his last witnesses. No court session is scheduled on Friday, which is a national holiday in South Africa.
"We foresee that we'll call four or five more witnesses and that we'll be able to close our case early next week," Nel said.
In other testimony Wednesday, police Col. Ian van der Nest testified that many of the blood spots and stains found in various parts of Pistorius' house were due to arterial bleeding, consistent with the gunshot wounds on Steenkamp's head and arm. Some stains came from Steenkamp's blood-soaked hair as well as her short pants, which had been saturated with blood, he said.
Another witness, Col. Mike Sales, investigated the web history on two iPad tablets found in Pistorius' home. He analyzed the activity on one of the devices hours before Steenkamp was killed, he said.
Around 6.30 p.m. South African time on Feb. 13, according to records shown on TV monitors in court, a search was made on Google for a pornographic website. Then, straight after, a page was accessed that was described with the words "Mobile Porn, Free Mobile Porn, iPhone Porn, Phone Porn, iPad Porn."