An emotional Oscar Pistorius has apologised to the family of girlfriend Reeva Steenkamp, on the first day of his evidence at his murder trial.
In a trembling voice, he said he was "trying to protect" her and said he could not imagine the family's pain.
Mr Pistorius said he suffered "terrible nightmares" and often woke up smelling Ms Steenkamp's blood.
Prosecutors say he killed her in February 2013 after an argument. He says he mistook her for an intruder.
The Paralympic athlete told Ms Steenkamp's relatives that 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."
In the packed Pretoria courtroom, Ms Steenkamp's mother, June, sat stony-faced while he spoke.
Mr Pistorius said he was taking anti-depressants and sleeping pills.
"I'm scared to sleep, I have terrible nightmares, I can smell blood and wake up terrified," he said.He added that he never wanted to handle a gun again.
The athlete, 27, told the court about his difficult childhood after being born with parts of both legs missing and needing to wear prosthetic limbs.
After a recess, Mr Pistorius was asked whether he and his family had been exposed to criminal acts.
He said there had been many break-ins while he was growing up.
Mr Pistorius said on one occasion he was followed by a car into his gated community. He said he had his gun with him and the two men in the car had sped off.
On another occasion, he said he had drawn his firearm as he tried to protect a taxi driver who was being assaulted.
Mr Pistorius testified: "They started beating him with rocks in his face and in his head. At that point I jumped the lights. I hooted until I pulled up. I drew my firearm. I pointed it at the three people. They jumped in the taxi. They sped off."
Mr Pistorius said he was also attacked at a party in December 2012, and had to have stitches in the head.
Mr Pistorius then detailed how important religion was to him, saying: "When I met Reeva, I think it was just a blessing. I've always wanted to have a partner that was a Christian. She was a very strong Christian."
He then became emotional again as he said "my God's a God of refuge" and his counsel, Barry Roux, asked for an adjournment.