FANTASY: Guild Wars is an online game that pits warriors and sorcerers against one another.

An online gamer is accused of killing his cyber-rival after losing a fantasy game where they were pitted against each other in battle.

The violent blurring of the virtual and real worlds came after the pair had been playing an online game, each in his own house kilometres apart.

The Sunday Star-Times cannot reveal the names of the accused killer nor his victim, where the homicide took place or when, because the details may prejudice an eventual trial.

However, police have confirmed they believe the most likely motive for the attack was the game which the pair played in the hours immediately before the attack.

The dead man favoured PC-based role-playing games such as Guild Wars and Oblivion, which create complex fantasy worlds filled with swords and sorcery.

Guild Wars, part of a genre gamers call MMORPG (massively multiplayer online role-playing games), focuses on highly competitive player-versus-player action.

Players can spend considerable time and effort building characters - gaining experience, weaponry, armour and in-game money to become more powerful.

Police believe that after a dispute arose, the attacker was so enraged he drove the short distance to the quiet street where his friend lived, and stabbed him repeatedly with a knife.

Despite the apparent link between the killing and the violent video game, Christchurch-based clinical psychologist Craig Prince said there was no evidence violent online games created killers.

"It's often very difficult to pinpoint which variable contributed to these things because people are so complicated," he said. "It's usually that people have some underlying difficulty or problem already and the video game might contribute to the actions, but it's only one thing out of potentially many."

The man has appeared in court charged with murder. His parents would not speak to the Star-Times but an extended family member said: "He's just lovely. It's such a shock... it's obviously the last thing we expected."

The relative, who described the alleged killer as "academic and quiet", confirmed he enjoyed computer games but did not think he had any obsessive gaming tendencies.

His parents were unconcerned about his behaviour in the lead-up to the incident.

"It was just the most regular of nights and there were no warning signs - it was just the hugest shock to everybody," the relative said.

If the gaming link is proved in court, it will put New Zealand on an international stage.

The supposed link between video games and violence, alternatively mooted and refuted in contradictory multiple reports in recent years, resurfaced in the wake of the Sandy Hook Elementary School massacre in Connecticut, in the US.

The parents of the victim were unavailable to comment but colleagues of the dead man said he worked in the IT industry and produced "remarkable" work, while staying totally humble. Workmates described him as "quiet but very, very clever". They confirmed he was an avid gamer.

Adam Lanza, 20, killed 20 children and six staff on December 14 last year. Police said Lanza had dozens of violent video games that he played regularly and they were looking into whether there was a link between the games and the shootings.