Oscar Pistorius was reduced to tears as he apologised to the family of Reeva Steenkamp, as he took the stand to give evidence in his murder trial.
The Paralympic athlete said he was not able to imagine the pain Mr Steenkamp's death has caused her family before claiming that he was "trying to protect" her on the night of her death.
Mr Pistorius also claimed that he suffered "terrible nightmares" in the weeks following the incident in which he shot and killed his girlfriend on Valentine's Day last year, and also claimed to smell her blood upon awaking.
Prosecutors accuse Mr Pistorius of deliberately killing the model, shooting her after she barricaded herself in the bathroom. Mr Pistorius denies the charge, insisting he thought she was an intruder.
Taking the stand to give evidence after a 10-day hiatus, Mr Pistorius addressed the family of the victim.
The 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."
Ms Steenkamp's mother, June, reportedly sat with a straight face throughout Mr Pistorius' speech in what was a packed courtroom in Pretoria.
The double leg amputee, who became the first Paralympian to compete in the Olympics in London, admitted he has been forced to using sleeping pills as a result of the incident.
"I'm scared to sleep, I have terrible nightmares, I can smell blood and wake up terrified," he said.
Mr Pistorius went on to talk about a childhood filled with the threat of break-ins, leaving him in a state of constant paranoia and also detailed similar events in his adult life.
Speaking of a moment where is saw a taxi driver being beaten, he said: "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."
The case continues on Tuesday.
If found guilty, the double-leg amputee could face life imprisonment.