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Pistorius told the court Reeva passed away in his arms Getty

Oscar Pistorius has described the moment Reeva Steenkamp died in his arms in a pool of blood after he gunned her down.

Giving evidence for the third successive day, the Bladerunner said he heard Steenkamp breathing as he held her after discovering he had fatally shot her.

He put his fingers in her mouth in a desperate attempt to help the model breathe as she lay dying.

In emotional scenes at North Gauteng High Court, Pistorius described finding his girlfriend, 29, slumped on the toilet bowl in his bathroom.

"I checked to put my arms under her shoulders and put her onto her knees and sat there crying for some time. I had her head on my left shoulder and could feel her blood running down on me," he said.

"At a point I heard her breathing so I swivelled around with my back against the back of the door and turned around so I could get to the door of the toilet so I could pick her up."

The Olympian and Paralympian paused as he struggled to contain his emotions, before continuing: "I could see her arm was broken. I was on my knees and placed her down and pulled one of the carpets closer and placed her head down softly on the carpet."

He then carried Steenkamp downstairs in a tragic scene described previously by neighbours during the murder trial.

"At that point I was shouting and screaming when I got to the bottom of the flight of stairs they told me to put Reeva down," the runner said.

"I said to them we need to get to the hospital. They said: "just put her down, the ambulance is on its way." I just sat with her and waited for the ambulance to arrive. I felt helpless.

"I had my fingers in her mouth to help her breathe. I had my hand on her hip to try and stop the bleeding."

The emergency services promptly arrived at the runner's luxury home on a gated complex outside Pretoria soon afterwards. But it was too late for them to help.

He was found sitting on the floor downstairs in floods of tears by police.

Pistorius said: "Reeva had already died while I was holding her, so I knew there was nothing I could do for her. The paramedic came to me and informed that Reeva has passed. I went downstairs and sat in the kitchen and sat on the floor crying.

"I don't know how much time passed at that point but some police officers arrived shortly thereafter."

Colonel Van Rensburg and other officers began investigating the scene while Pistorius was slumped in a heap on the floor. He asked them for permission to wash his hands of Steenkamp's blood because it was making him retch.

Pistorius then waited in the garage for "several hours" with police. Rensburg finally informed him he was under arrest.

"It was at that point Col Van Rensbug told me, as I was the only person in the house, they were going to charge me, he said I was under arrest."

Pistorius denies murder and claims he mistook Steenkamp for an intruder. The prosecution alleges he killed her following an argument between the couple.

The trial continues.