Stander had entered the home after Pistorius called him to the house for help and said he found Pistorius over Steenkamp's body trying to save her life and in shock over what had happened.
"I received a call from Mr. Pistorius and he said on the call, ‘Johan, please, please, come to my house, please. I shot Reeva. I thought she was an intruder. Please come quick,'" Stander told the court.
"His commitment to save the young lady's life, when he put his finger in his mouth and tried to keep the airway open, went to breathe," said Stander in his testimony. "How he begged her to stand with him, how he begged God to keep her alive...no. I saw the truth there that morning. I saw it. And I feel it."
Stander's daughter, Carice Viljoen, also testified and said that when she entered the house with her father, there was blood everywhere and Pistorius was begging to take her to the hospital. At one point, she said she was afraid he was going to use the gun to shoot himself.
Pistorius has broken down in tears several times in court and even vomited when the photos of Reeva Steenkamp's body were shown during the trial.
The verdict is expected to come at the end of May or early June.
Notable deaths of 2014 [PHOTOS]