(CNN) -- Three bangs. Four shots. Nine witnesses.
"Blade Runner" Oscar Pistorius has been on trial for a week, charged with the murder of his girlfriend, model Reeva Steenkamp.
At this point, some facts are beyond dispute.
The Olympic and Paralympic track star killed his girlfriend in the early hours of Valentine's Day last year. He fired four bullets through the door of a toilet room she was in. Three hit her; the final one in the head, and she died.
The overarching question in the trial is why he did it. He says he thought she was a burglar and made a tragic mistake. Prosecutors say the couple argued and he shot her in anger.
In the first week of the trial, it became clear that the judge's verdict would hinge on several questions that, so far, remain unanswered:
What were the bangs that neighbors heard on the night of the shooting?
Four people who live near Pistorius said they heard loud bangs on the night of the shooting, with a pause between them. All four -- Michelle Burger, Estelle van der Merwe, Charl Johnson and Johan Stipp -- said they thought at the time that the sounds were gunshots.
They generally agree that there was a pause between two distinct sets of bangs or booms, with screaming in between.
Defense lawyer Barry Roux argues that the second set of bangs was in fact the sound of Pistorius breaking down the toilet door with a cricket bat after he realized what he had done.
But Burger and Stipp said the three bangs they heard came in such quick succession that there would have been no time to swing the cricket bat back before striking the door again.
Does Pistorius sound like a woman when he screams?
There were some chuckles in court when Roux first asserted that Pistorius sounds like a woman when he screams, but it turns out to be a critical part of the defense.
Some witnesses testified to hearing screams before any of the bangs, including the sound of both a man and a woman shouting.
The prosecution argues that the screaming was the argument that led Pistorius to murder Steenkamp.
But there was a second scream or series of screams that the neighbors said sounded like a woman in terror. Burger called them "petrifying," and Stipp said the woman sounded "scared, almost scared out of her mind."
That screaming, the prosecution suggests, was Steenkamp fleeing in fear from an enraged Pistorius.
But the defense says it was Pistorius himself, screaming in anguish as he realized his deadly error.
Neighbor van der Merwe gave some support to this theory, saying she heard what she thought was a woman screaming and asked her husband what it was. Her husband, who knows the track star, told her it was Pistorius, she testified.
But Samantha Taylor, an ex-girlfriend of Pistorius, testified that he had yelled at her and others often and that when he shouted, he sounded like a man.
Is Pistorius trigger happy?
This is a key element of the state's case, which prosecutor Gerrie Nel admitted in his opening statement is "circumstantial" -- there were no eyewitnesses to the killing.
So the state has brought two unrelated gun charges against Pistorius -- one that a gun went off in a crowded restaurant when he was holding it, and one that he fired a gun out a car's sunroof in irritation after an aggravating police stop for speeding that turned into an argument over his gun.
It's not clear that the prosecution witnesses who have talked about the two incidents have done much to build the state's case.
Boxer Kevin Lerena, a friend of Pistorius, was with him at the restaurant, he testified. Lerena said a third friend, Darren Fresco, passed Pistorius a loaded gun under the table, telling the athlete he was "one up." That meant there was a bullet in the chamber of the gun, ready to fire. Almost immediately, it went off under the table. Pistorius apologized to his friends and asked Fresco to take the blame, which he did in order to avoid drawing attention to the Blade Runner.
Taylor is the only source for the sunroof incident thus far, and she was unable to provide any details about where it took place. Roux said that Pistorius was in fact golfing at St. Andrews in Scotland the day after Taylor said it happened.
But Taylor also said that Pistorius carried a gun with him and that at least once when he heard a noise at his bedroom window at night, he woke her, took his gun and went to investigate. Another time when he thought his car was being followed, she said, he took his gun and knocked on the window of the other car with it.
Did Pistorius lie to a security guard after killing Steenkamp?
The ninth and last witness of the week was Pieter Baba, who was on duty as the security shift supervisor at the Silverwoods Estate on the night Pistorius shot Steenkamp. Several neighbors called his office to report hearing gunshots, and Baba went out with another guard to investigate. He ended up near the Pistorius house, speaking to Pistorius on the phone.
According to Baba, Pistorius said: "Security, everything is fine." But Baba could hear Pistorius crying and decided to go to the house. He arrived in time to see Pistorius carrying Steenkamp's body down the stairs. "My lady, I was so shocked I couldn't think for a few moments," he told the judge.
Roux made a concerted effort to shake Baba's version of what Pistorius said on the phone, asking twice in a row whether the runner had said "everything" was fine or that "he" was fine, then whether he had said "OK" or "fine."
Baba stuck to his story and finally turned to the judge to say: "My lady, Mr. Pistorius's exact words were, 'Security, everything is fine.' "
Testimony for the week ended on that note, with Baba to continue on the stand Monday.
Why do South Africans call security rather than the police when they hear gunshots?
South Africans who can afford it tend to live in areas with private security. Their alarm systems alert their private security guards, not police.
South Africans who use private security say their guards are based closer and will be on the scene faster than police.
Of the four Pistorius neighbors who testified, only one, Stipp, said he called police -- and even he called private security first. He said that the estate's security guards arrived soon after he called, and that after talking to them, he went to the house to see if he, a doctor, could help.
He found security guards there and told them to call an ambulance. He left after the ambulance team did, by which time police still had not arrived.