Pretoria, South Africa (CNN) -- Prosecutors trying to prove that Oscar Pistorius murdered his girlfriend Reeva Steenkamp appeared to have won a round on Tuesday morning, but it was the defense team that was smiling by the end of the day.
Tuesday's testimony began with the expert who conducted the autopsy on Steenkamp, Gert Saayman. He backed two key points of the state's case.
He estimated that Steenkamp had eaten about two hours before she died, which contradicts Pistorius' version of events, and he said that the victim would have been able to scream after the first two bullets hit her, as the prosecution argues.
"I think it would be somewhat abnormal if one did not scream when sustaining a wound of this nature," Saayman testified of the "particularly devastating" injury to Steenkamp's right arm.
A day earlier he described in graphic detail the damage that Pistorius' bullets did to Steenkamp's body, leaving the defendant vomiting, dry heaving, weeping and clutching his head in his hands.
Pistorius, 27, was calm in court on Tuesday.
He pleaded not guilty to murder, although he admits killing his 29-year-old girlfriend by shooting her through a locked bathroom door. He mistook her for a burglar in his house in the middle of the night, he maintains, saying he made a tragic but understandable mistake.
The prosecution is trying to build a circumstantial case that Pistorius is trigger-happy and that the couple argued before he killed her.
Pistorius is also charged in connection with two other alleged incidents of guns going off in his hands, unrelated to the killing of Steenkamp.
Pistorius' friend Darren Fresco, who was present for both incidents, was on the stand for the state most of the day on Tuesday.
A furious Pistorius fired a gun from a car sunroof after a police officer handled his weapon during a traffic stop, Fresco testified.
Fresco was driving the car in late 2012 when police pulled him over for speeding.
"(The) officer had picked up the accused's weapon, to which the accused said 'You can't just touch another man's gun,'" Fresco said.
"He was furious about it, that someone else had touched his gun," Fresco said. Pistorius later that day fired through the sunroof "out of the blue ... no warning," he said.
On Friday, Pistorius' ex-girlfriend Samantha Taylor testified about the sunroof shooting incident, saying the two men laughed and joked about shooting a "robot," a traffic light, before the gunfire. Fresco denied he had been joking with Pistorius before the gun went off.
Fresco also testified about an incident at Tashas Restaurant, where Pistorius is accused of asking him to take the blame after he discharged Fresco's pistol under the table one month before Steenkamp's death.
Fresco told defense lawyer Barry Roux that his written witness statement was prepared with a lawyer's help "to make sure I wasn't going to put myself into any kind of trouble," but he insisted it was the truth.
Judge Thokozile Masipa told Fresco he would be immune from prosecution for self-incriminating testimony if he tells the truth.
At times Tuesday Fresco seemed evasive, insisting he did not remember what happened after dinner on the night of the sunroof incident, despite having described the day in detail up to that point.
At other times he got testy with the acerbic Roux's cross-examination, saying he did not have a ruler with him when Roux asked how close he and Pistorius were when the gun changed hands at Tashas.
And there were sharp intakes of breath in court toward the end of the day when Fresco let slip that he had been following some of the trial on Twitter.
Fresco had volunteered on the stand that he was not wearing "tracksuit bottoms" at Tashas because it was summer.
Roux pounced, asking who had said anything about tracksuit bottoms.
"People have said to me, 'Your name's been mentioned; your name's been mentioned; your name's been mentioned," Fresco said. "I wanted to find out what was said."
Witnesses are not supposed to listen to the testimony of other witnesses in order to keep their testimony from being tainted.
Gun at his bedside
The case against Pistorius is largely circumstantial, prosecutor Gerrie Nel conceded in his opening statement last week. Pistorius and Steenkamp were the only people in his house when he killed her in the early hours of Valentine's Day 2013.
Nel has been building a picture of what happened through the testimony of neighbors who heard screaming and bangs that night, current and former friends of the South African track star, and a security guard who sped to the scene because of reports of gunshots.
Defense lawyer Roux has gone after holes, doubts, discrepancies and inconsistencies in prosecution witness stories. He is trying to sow reasonable doubt that their memories of events are correct.
Many prosecution witnesses' stories are consistent with Pistorius' version of events, that he got up in the night, went out to his balcony to get a fan, came back inside, and heard noises in the bathroom that he thought to be an intruder.
He said he took the gun and fired while calling for Steenkamp to call the police. When she didn't answer he realized it could have been her in the bathroom, he said.
Taylor, his former girlfriend, testified Friday that he reacted similarly once when she was sleeping at his house.
She said Pistorius, the first double-amputee to run in the Olympic Games, once heard something hit a bathroom window and woke her up to ask if she'd heard it, too, before taking his gun and going to investigate. Taylor said Pistorius woke her up other times when he thought he'd heard a noise.
Taylor also testified that Pistorius slept with a pistol on his bedside table or on the floor beside his prosthetic legs, and he once became so angry after a traffic stop that he shot a gun through the sunroof of a car.
Prosecutors appear to have been trying to demonstrate that Pistorius and Steenkamp had a loud argument before the shooting, suggesting it's the reason he killed her.
Neighbors said they heard a woman screaming before the shots were fired. But the defense is proposing that what neighbors thought was Steenkamp screaming in fear for her life was in fact Pistorius when he realized what he had done.
Pistorius and at least two neighbors made phone calls to security after the shooting, allowing the defense to use phone records to establish a timeline of events.
Masipa will decide Pistorius' verdict. South Africa does not have jury trials.
In South Africa, premeditated murder carries a mandatory life sentence with a minimum of 25 years. Pistorius also could get five years for each gun indictment and 15 years for a firearms charge he also faces.
If he isn't convicted of premeditated murder, the sprinter could face a lesser charge of culpable homicide, a crime based on negligence. The sentence for culpable homicide is at the judge's discretion. The trial is expected to take at least three weeks.
CNN's Richard Allen Greene reported from Pretoria, Marie-Louise Gumuchian wrote from London. CNN's Ed Payne and Emily Smith also contributed to this report.