An emotional Oscar Pistorius has apologized to the family of his 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 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.