Oscar Pistorius tearfully apologised to the family of model Reeva Steenkamp on Monday (07Mar14) as he revealed his nightmare world of anti-depressants and sleepless nights since shooting her dead.

The embattled South African Paralympian, who is on trial accused of murdering Steenkamp in February last year (13), took to the stand on Monday to begin his defence.

He was weeping as he entered the witness box and was heard saying, "Oh help me God", before launching into an apology to the model's family.

Racked with sobs and barely able to speak coherently, Pistorius told the court, "I would like to take this opportunity to apologise to Mr. and Mrs. Steenkamp, to Reeva's family, to those of you who knew her and are here today.

"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're the first people I think of. The first people I pray for. I can't imagine the pain or the sorrow and the emptiness that I've caused you and your family. I was simply trying to protect Reeva. I can promise that when she went to bed that night she felt loved."

Pistorius then revealed he has been taking anti-depressants and sleeping pills since the shooting, adding, "I am scared to sleep... I have terrible nightmares about what happened that night. I wake up and I can smell blood."

Earlier on Monday, Pistorius openly sobbed and retched as pathologist Professor Jan Botha described the effects of gunshots on 29-year-old Steenkamp.

Pistorius, 27, is accused of intentionally gunning down his model girlfriend through a bathroom door at his South African home, but he claims he shot her by accident after mistaking her for an intruder.

He denies one charge of murder and three firearms offences.