Oscar Pistorius gestures as he listens to evidence today in court in Pretoria, South Africa.

PRETORIA, South Africa — Stifling sobs, Oscar Pistorius took the witness stand today in his murder trial and apologized to the family of the girlfriend he shot dead, describing himself as being traumatized and awakening from nightmares to the “smell of blood.”

Pistorius’ voice quavered so much and was so low that Judge Thokozile Masipa asked him to speak up to the packed courtroom as he described his remorse for having killed Reeva Steenkamp on Feb. 14, 2013.

He said he mistook her for an intruder when he fired four times through a locked toilet stall door in his home. Prosecutors said he shot her as she screamed in terror after they had an argument in the predawn hours of Valentine’s Day.

“There hasn’t been a moment since this tragedy happened that I haven’t thought about your family,” the double-amputee star athlete said as he addressed the courtroom and Steenkamp’s mother, June, who looked straight at him, stone-faced.

“I wake up every morning and you’re the first people I think of, the first people I pray for ... I was simply trying to protect Reeva. I can promise that when she went to bed that night she felt loved,” Pistorius said.

Prosecutors allege the Olympian murdered her with premeditation by shooting her in the head, arm and hip after an argument and have sought to paint him as a hothead with an inflated sense of entitlement and an obsession with firearms.

In his testimony, Pistorius also said he is on antidepressant medicine and now has trouble sleeping.

His testimony on day 17 of his trial in Pretoria came on the same day his defense opened its case. Legal experts said it was crucial to his case that he testify to explain why he shot Steenkamp.

Pistorius faces 25 years to life in prison if convicted of premeditated murder for Steenkamp’s killing.