Olympic and Paralympic track star Oscar Pistorius sits in the dock on the third day of his trial for the murder of his girlfriend Reeva Steenkamp at the North Gauteng High Court in Pretoria. Photo: Alon Skuy/Reuters

Pretoria - Murder accused Oscar Pistorius was sincere in his grief after he shot and killed his girlfriend Reeva Steenkamp, the High Court in Pretoria heard on Thursday.

Radiologist Johan Stipp told the court he found Pistorius was emotional as he tried to revive Steenkamp at the bottom of the stairs at his Pretoria home.

“He definitely wanted her to live... He looked sincere to me. He had tears on his face,” said Stipp.

Stipp lived close to the Pistorius home at the Silver Woods Country Estate where the paralympian shot dead Steenkamp on Valentines' Day last year.

He said he arrived at Pistorius's home shortly after the shooting and found Steenkamp's body lying at the bottom of the stairs with Pistorius trying to clear her airway.

Stipp said he attempted to help, but soon realised Steenkamp was dead.

“He was crying... He was praying and making promises to God. He was distraught,” Stipp told the court,

In his official statement, he had described Pistorius as being “beside himself”.

Listening to the testimony Pistorius appeared to be crying, clutching his hands onto his head. His sister Aimee walked into the dock and sat next to him.

She spoke to him as he continued to cover his eyes.

He has maintained that he shot her thinking she was an intruder.

The State will try to prove that Pistorius committed premeditated murder when he shot Steenkamp through the locked bathroom door at his home.

Pistorius's lawyers will argue that he mistook her for an intruder when he shot through the bathroom door.

In addition, Pistorius is charged with the illegal possession of a firearm and ammunition.