After four weeks of prosecution-led testimony and one week's adjournment, Pistorius took to the stand Monday for the first time to explain his version that he shot and killed his girlfriend Reeva Steenkamp by mistake on Valentine's Day last year.

Pistorius began his testimony by apologizing to Steenkamp's family, many of whom were sitting in the public gallery.

"There hasn't been a moment since this tragedy happened that I haven't thought about your family. I wake up every morning and you are the first people I think of," he told the court, his voice audibly shaky.

"I can't imagine the pain and emptiness I caused you and your family. I was simply trying to protect Reeva. When she went to bed that night she felt loved," he said. Live images from the court were broadcast with an audio-feed of Pistorius. He was, however, not shown on camera.

The Paralympian told the court he has been on anti-depressants and sedatives since killing Steenkamp. "I have terrible nightmares about things that happened that night, where I wake up and I can smell blood," he said.

Proceedings were halted early after Pistorius' lawyer Barry Roux said his witness was exhausted by a lack of sleep and the day's testimony.

Pistorius has pleaded not guilty and maintains he mistook 29-year-old model and law graduate Steenkamp for an intruder when he fired four rounds through the locked toilet door in his upscale Pretoria home. The prosecution has accused Pistorius of deliberately killing Steenkamp after an argument.

Pathologist testifies

The first witness to testify on Monday, before Pistorius, was forensic pathologist Prof. Jan Botha, called to the stand by Roux.

In his testimony, Botha disputed evidence by the prosecution's forensic pathologist who said that matter in Steenkamp's stomach suggested she ate two hours prior to her death, an event that conflicts with Pistorius's version of events.

Botha said the timeframe of when Reevkamp ingested the food "could have been an hour or two, or it could have been significantly longer." He said determining the time of death through gastric emptying is guesswork, calling it a "highly controversial and inexact science."

Nicknamed "Blade Runner," Pistorius was the first double leg amputee to compete against able-bodied athletes in the 2012 London Olympics. A top Paralympic performer since 2004, he went on to win two gold medals and a silver medal at the Paralympics in London.

The case has garnered international attention as the world’s most high-profile trial involving an athlete since the case of American football star OJ Simpson in the mid-1990s.

Judge Thokozile Masipa will pronounce Pistorius innocent or guilty and decide on any sentence as there is no trial by jury in South Africa. If convicted, prosecutors say they will seek a life sentence, which would require Pistorius to spend a minimum of 25 years in prison.

hc/msh (Reuters, AFP, AP)