End in sight for Oscar Pistorius murder trial: 'I did not intend to kill Reeva'

(CNN) -- After nearly 40 days of testimony, several unexpected delays and the defendant's 30-day stint in a mental health facility, the Oscar Pistorius trial is finally nearing an end.

Closing arguments are scheduled to begin Thursday in the case against the double amputee Olympic sprinter who is on trial in South Africa for premeditated murder in the death of his girlfriend, Reeva Steenkamp.

Prosecutors have alleged that Pistorius, 27, was engaged in a heated argument with Steenkamp in the early morning hours of February 14, 2013, before he intentionally pulled the trigger of his gun and shot through a closed bathroom door, ending her life.

But Pistorius says he heard a noise coming from his bathroom that morning, that he felt vulnerable without his prosthetic legs on and that he mistook Steenkamp for an intruder. He says he accidentally shot her four times.

Here are some of the biggest moments from the trial, which began in March:

Pistorius weeps on the stand, tells his side

"I did not intend to kill Reeva my lady, or anybody else, for that matter," Pistorius told the judge in March as he recounted the tragic events that unfolded on Valentine's Day 2013.

He described how he was awakened by -- and went to investigate -- a sound coming from his bathroom in the early morning hours.

"That's the moment that everything changed," Pistorius testified. "I thought that there was a burglar that was gaining entry into my home."

Pistorius said he grabbed his gun and whispered for Steenkamp to get down and call police. He said he heard the toilet door close, confirming someone was inside, and that he thought that a person (or people) was about to come out and possibly attack him.

"Before I knew it, I'd fired four shots at the door. My ears were ringing. I couldn't hear anything," he said.

Prosecutor Gerrie Nel spent several days grilling Pistorius during cross-examination. He narrowed in on the details of Pistorius' testimony, in an attempt to chip away at his story.

Nel accused Pistorius of lying, said that Pistorius planned to kill Steenkamp and even surprised him by unexpectedly flashing a picture of Steenkamp's body on the courtroom monitors.

"I don't have to look at a picture -- I was there," Pistorius told the judge as Nel demanded he view the image and take responsibility for what he had done.

Battle of the neighbors: What exactly did they hear?

Neighbors who testified for both the prosecution and the defense agree they heard shouting and bangs in the early morning hours. The source of those noises, however, has been disputed and may turn out to be one of the pivotal issues of the case.

Several neighbors called by the prosecution said they heard "loud voices" arguing before the fatal gunshots rang out in their affluent South African neighborhood.

"The intensity and fear in her voice escalated and it was clear that her life was in danger," neighbor Charl Johnson testified. "The last scream faded moments after the last shot was fired."

The defense, however, called more neighbors -- who lived closer to Pistorius -- to testify in an attempt to show that the prosecution's witnesses were mistaken in what they heard that night. Two of the defense's witnesses even re-created the sounds they heard, which they said were the cries of a man seeking help.

The defense has suggested this was the source of the voices the other neighbors heard and that the bangs they heard after were not gunshots but the sounds of Pistorius trying to break down the bathroom door with a cricket bat.

Judge orders Pistorius to undergo a psychiatric evaluation

When the defense's psychiatrist, Merryll Vorster, testified in May about diagnosing Pistorius with an anxiety disorder, the prosecution pounced, telling the judge they needed an independent psychiatric evaluation.

Vorster had suggested the disorder could have contributed to Pistorius' judgment on the night he shot and killed Steenkamp. The judge ruled that Vorster raised the issue of Pistorius' mental health, which needed to be examined further.

Pistorius was admitted as an outpatient at a state-run facility and underwent a 30-day mental health evaluation.

The results of the panel's report had the potential to make a major impact on the outcome of Pistorius' trial. While his defense did not argue that he was insane or mentally incapacitated at the time of the shooting, it was possible the doctors would find that he was. This left open the possibility the trial would end immediately if Pistorius was found not guilty by reason of mental illness.

Docs say Pistorius is depressed, but knew what he was doing

After about a month and a half of waiting, the trial resumed, and the results of Pistorius' psychiatric evaluation were read aloud in court: He was not mentally ill when he shot and killed Steenkamp, according to the doctors.

They additionally found that Pistorius suffers from post-traumatic stress disorder, is depressed and a suicide risk. But even so, Pistorius knew what he was doing on the night of Steenkamp's death, they said.

Doctors additionally said they believed Pistorius is not narcissistic or psychopathic, he has no history of violent behavior or abusive relationships, and he was "severely traumatized" by shooting his girlfriend.

Delays put the trial on hold

The 30-day psychiatric evaluation was just one of several delays in the trial.

In March, the judge announced that a crucial member of the court, called an assessor, was sick and had to be hospitalized. In South Africa, there are no juries. Instead, there is a single judge who is assisted by two lay people called assessors, who have expertise in the issues being presented in court. While these assessors may have some legal training, they are there to help the judge decide on matters of fact, not the law. Court was delayed for a week because of her illness.

Pistorius' own testimony caused a brief delay in March. "She wasn't breathing," he managed to choke out before breaking down in sobs on the stand. The judge ended court early for the day.

Pistorius' trial also took a two-week break at the end of March, at the prosecution's request. The proceedings had already gone longer than they had expected at this point, and one of the state's counsel was a part of another trial that involved a person being held without bail. Since Pistorius is out on bail, the other person's legal matters took precedence over Pistorius'.

Finally, after the monthlong mental health evaluation, the defense rested its case in July. Closing arguments were scheduled next, but both sides were given about a month to prepare. Such a lengthy pause was likely granted so both sides would have time to read the court reporter's transcript of the case, according to CNN legal analyst Kelly Phelps. It was estimated to be as long as 4,000 pages.

So, what happens next?

Since there are no juries in South Africa, Pistorius' fate rests in the hands of Judge Thokozile Masipa. If an assessor who is advising her disagrees with the verdict, he or she can write a dissenting opinion. The two assessors can also, in theory, overturn the judge's ruling, although this doesn't happen in practice.

If the judge rejects Pistorius' claim that he believed he was shooting at an intruder, then she could find him guilty of murder and sentence him to a prison term ranging from 15 years to life (there is no death penalty in South Africa).

If she accepts that Pistorius did not know that Steenkamp was the person he was shooting at, she could find him guilty of culpable homicide, a lesser charge than murder, or acquit him, according to Phelps, the CNN legal analyst. In this last case, the sentence would be up to the judge's discretion.