Oscar Pistorius has apologised to Reeva Steencamp's family for her death.

The Paralympic athlete started his murder trial testimony today (07.04.14) by offering his condolences to his late girlfriend's parents, apologising for the pain and ''emptiness'' he has caused the model's loved ones by shooting her through the bathroom door at his home in Pretoria, South Africa, on 14 February 2013.

The London 2012 medallist claims he mistook Reeva for an intruder in the bizarre incident, while prosecutors allege he killed her in cold blood.

Fighting back tears, Pistorius said in a trembling voice: ''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 and 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. I've tried to put my words on paper many, many times to write to you. But no words will ever suffice.''

His words seemed lost on the blonde's mother, June, who sat in the courtroom stony-faced throughout.

Pistorius confessed he had been suffering from horrific nightmares ever since the incident and had been taking anti-depressants and sleeping pills.

The 27-year-old star said: ''I'm scared to sleep, I have terrible nightmares, I can smell blood and wake up terrified.''

He also revealed he never wanted to hold a gun again and discussed the importance of religion in his life, the BBC is reporting.

Today marks the first day of the defence case, with the troubled athlete's lawyer Barry Roux explaining he would be calling on 14 to 17 witnesses to testify on ''ballistics, urine emptying, damage to the toilet door, sound, and disability and vulnerability''.

There has already been 15 days of prosecution-led testimony which has seen testimonies from neighbours and ballistics experts, as well forensic and mobile phone evidence.