Prosecutors are seeking to prove that the Olympic and Paralympic athlete tried to kill Steenkamp deliberately by firing four rounds from a 9 mm pistol through a locked toilet door after a heated argument.
Pistorius, nicknamed the "Blade Runner" due to his carbon-fiber prosthetic limbs, has pleaded not guilty, saying he was deeply in love with 29-year-old Steenkamp and that he mistook her for an intruder hiding in a toilet at his luxury Pretoria home.
Defense lawyers spent much of Tuesday going through some of the thousands of text messages the pair sent each other in the weeks before Steenkamp's death to focus on their "loving relationship".
A day earlier, police expert Francois Moller read out a series of retrieved messages that painted a picture of a volatile, stormy relationship, with Steenkamp accusing Pistorius of continual jealousy and outbursts of anger.
"I'm scared of you sometimes and how you snap at me and of how you will react to me," one message sent by Steenkamp on January 27, 2013 said.
Moller said despite the arguments, 90 percent of the messages were normal, often loving, interactions.
Defense lawyer Barry Roux pointed to an exchange on January 19 in which Steenkamp sent Pistorius a photo of herself blowing a kiss into the camera, followed by the question: "You like it?"
"I love it," Pistorius replied.
Roux also showed CCTV footage from nine days before Steenkamp's death that showed the couple kissing in a convenience store, followed by another text exchange between them.
"I miss you one more than you miss me," the message from Pistorius read.
Pistorius' lower legs were amputated as a baby but he went on to achieve global fame as the "fastest man on no legs," winning gold medals at the Beijing and London Paralympics.
He also won a battle against athletics authorities for the right to compete against able-bodied men, becoming the first amputee runner at an Olympics when he reached the 400 meters semi-finals in London 2012.
The court adjourned until Friday, when the defence will start revealing its own argument and evidence in support of Pistorius' innocence.
The 27-year-old is expected to take the stand in his own defence - a high stakes gamble that could backfire if holes start to emerge in the version of events he submitted in sworn testimony at his bail hearing a year ago.
If found guilty of murder, he faces at least 25 years in prison.
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