The waiting will end for Oscar Pistorius on Thursday morning when a high court judge delivers her verdict on whether the Paralympian is guilty of murdering his girlfriend Reeva Steenkamp.

Millions around the world are expected to listen on television, radio and online as judge Thokozile Masipa makes a ruling that could either condemn Pistorius to long years behind bars or allow him to resume his extraordinary athletics career.

After 41 dramatic court days spread over six months, and in the absence of a jury, Masipa will finally pass judgment on what happened at Pistorius's luxury home in Pretoria, South Africa, just after 3am on Valentine's day last year. There is no dispute that he fired four hollow-tipped bullets through a locked toilet door, killing Steenkamp, a model and law graduate, almost instantly. The question is why. The judge must weigh the prosecution's assertion that he murdered her in rage after an argument against the defence's case that he panicked after mistaking her for an intruder.

It has been one of the most sensational murder trials in recent years, often compared with that of American athlete and actor OJ Simpson. Prosecutors described Pistorius as an egotistical liar, obsessed with guns, fast cars and beautiful women, who was not prepared to take responsibility for his actions. The defence said there are "two Oscars" – a world-class athlete and a highly vulnerable individual with a serious disability who acted out of fear, not anger, when he fired the fatal shots. Pistorius frequently sobbed, howled and vomited in court.

"It is very traumatic," said Cassandra Fani, 24, a former athlete who used to train with Pistorius and supported him in court. "You're everyone's number one hero and the next minute you're everyone's enemy. Whether he comes out guilty or not guilty, his career is forever tainted. Everyone will think he's a murderer – the media have put that out there."

Members of both Pistorius's and Steenkamp's families will be out in force on the front row of the public gallery. But the start of the hearing on Thursday morning is likely to be something of an anticlimax for the eager global audience.

Masipa will read a written judgment in full and announce her verdict only at the end. She is expected to summarise the testimony of each of the 37 witnesses and make a finding on its credibility and applicability to the case. She is also likely to make reference to case law and will consider the three lesser firearms charges against Pistorius. The entire process will probably take at least a day. It therefore seems likely that she will not make her verdict known until Friday.

There are various possible verdicts available to the judge. She could find Pistorius guilty of murder, then specify whether it was premeditated (he intended and planned it), dolus directus (it was his aim and object to kill the deceased) or dolus eventualis (he foresaw the possibility of killing but did so anyway). Premeditated murder carries a mandatory life sentence whereas the other categories allow her wide discretion. There is no death penalty.

A further option is culpable homicide (manslaughter), meaning that Pistorius lacked intention but was negligent by the standards of a reasonable person. Legal experts have debated whether there could be a distinction between a reasonable person and reasonable disabled person, since the defence made much of Pistorius's lifelong feeling of vulnerability without his prosthetic limbs.

If Pistorius is convicted, he will have to reapply for bail since he will potentially be more of a flight risk. There will then be an adjournment, probably for a few weeks, before further arguments and sentencing. Pistorius would have the option to appeal so could potentially remain at liberty for months or even years.

A final possibility is that the 27-year-old, known as the "Blade Runner", will be acquitted if the judge accepts that he genuinely feared for his life and thought he was acting in self-defence. Depending on the three other charges against him, which include firing a gun in a restaurant, he could walk free and into a media maelstrom. His family have spoken of their hopes that he will resurrect his sporting career in time for the 2016 Olympics and Paralympics in Rio.

But few analysts following the trial believe that the sprinter, the first amputee to compete on an Olympic track, will escape a custodial sentence. "I have little doubt he will be convicted on a charge of murder," said Johan Burger, a former police officer and now a senior researcher at the Institute for Security Studies in Pretoria.

"It may not be premeditated murder. I'm not convinced the prosecution was able to prove beyond reasonable doubt that he knew it was Reeva Steenkamp in the toilet. But it is murder. He knew he would probably kill whoever was in there. I think he will get a prison sentence of a number of years."

A source close to the prosecution admitted there are holes in its case but said the same is true of the defence, and Pistorius should be convicted on his own version alone. Another legal observer commented: "Oscar's heart must have sunk when he heard judge Masipa would be running the trial. She is a hanging judge. She has been very tough on men who killed women in the past."

Pistorius's family, however, have loyally defended his integrity and version of events since the beginning. His uncle, Arnold Pistorius, insisted: "He's not a thief, he's not a liar, he's not a murderer." He was scathing of the prosecution case: "What's the saying? You can fool some of the people some of the time but you can't fool all of the people all of the time."

While an acquittal would bring relief for Pistorius, there is unlikely to be any sense of joy. Arnold added: "His sentence has been harsh already. Every cent gone. He's been punished tremendously. He lost his girlfriend and he's in mourning."