Oscar Pistorius’s murder trial has resumed in Pretoria, South Africa, with the start of the defense case.

Oscar Pistorius’ defense team called on pathologist Jan Botha as its first witness after a week’s adjournment.

The Paralympic athlete is expected to take the stand after Jan Botha to tell the court how and why he shot his girlfriend Reeva Steenkamp.

Prosecutors say Oscar Pistorius killed Reeva Steenkamp after an argument. He denies shooting deliberately, saying he mistook her for an intruder.

The trial was postponed for a week after one of the assessors assisting the judge fell ill.

Oscar Pistorius’s murder trial has resumed in Pretoria with the start of the defense case

Under South African law, there is no jury system and two assessors, normally lawyers or retired magistrates, help the judge reach a decision in serious cases.

The trial has already heard 15 days of prosecution-led testimony, which has relied on accounts from neighbors and specialist ballistics experts, as well forensic and mobile phone evidence.

One neighbor, Michelle Burger, told the court she was awoken by a woman’s “terrible screams” followed by gun shots.

Oscar Pistorius aims to convince the court that the screams were his, and that he shot Reeva Steenkamp through a closed toilet door because he had mistaken her for an intruder.

Defendants who choose to testify are the first defense witnesses in South Africa but Jan Botha was allowed to testify first because of a family illness.

It is thought that Oscar Pistorius will go next. He had been expected to take the stand when the trial was postponed on Friday, March 28.

The defense is also likely to address key questions, including allegations that Oscar Pistorius was reckless with guns and why he did not check the whereabouts of his girlfriend before he opened fire.

Reeva Steenkamp, a 29-year-old model, reality TV celebrity and law graduate, was hit by four bullets while in the toilet cubicle of Oscar Pistorius’ home in Pretoria on February 14, 2013.

Oscar Pistorius, 27, is a double amputee who holds six Paralympic medals and competed in the 2012 Olympic Games.

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