Nicholas Gera spent more than an hour wandering through a Sliema penthouse before entering the bedroom of the unsuspecting family in the early morning of New Year’s Day 2012, Police Commissioner Peter Paul Zammit believes.

The 26-year-old took the time to smoke a cigarette as he roamed the 500-square-metre apartment, using the light from an aquarium to find his way around before arming himself with two large knives and walking into the main bedroom.

What ensued was a horrific incident that shocked the nation – Mr Gera and Duncan Zammit, who had been asleep with his wife Claire Zammit Xuereb and their three-month-old twins, had a violent fight that left both men dead.

Duncan Zammit, 32, died of nearly 30 knife wounds, cuts and bruises – mostly sustained as he tried to defend himself – while Nicholas Gera had 10, although just two wounds could be considered life-threatening.

Police are still trying to piece together the intricate puzzle of clues, yet nearly two years on they are no closer to establishing a clear motive. They are now seeking foreign experts’ help in putting together a psychological profile of Nicholas Gera.

We have never succeeded in establishing a link between the two men and we’ve gone back years

“The question of why this happened will remain a mystery. The perpetrator is dead and he took the answers with him,” Mr Zammit tells The Sunday Times of Malta.

However, the Police Commissioner is convinced Nicholas Gera never entered the apartment to steal or kill and it could be the young man got sucked into a “dark psychological space” that ended with the deaths of the two men.

The police have failed to establish a link between the two men, but Mr Zammit is hoping to better understand what happened once he gets the psychological profiling of Nicholas Gera after Christmas.

‘Leaving cases like this one open isn’t healthy’

Since he took over the force earlier this year, Mr Zammit started re-evaluating a case that has fed numerous conspiracy theories.

“Leaving cases like this open-ended isn’t healthy for society – people need answers. This has been a tragedy of misconceptions,” he says.

One of the angles police pursued was the possibility of mistaken identity. The penthouse next door to Claire and Duncan had been temporarily used by a Serb and, since Nicholas Gera was adopted from Bosnia, police explored this possible link. But the theory came up dry.

One of the facts people found hardest to swallow is that Nicholas Gera and Duncan Zammit did not know each other. Despite re-examining the case, the Police Commissioner still believes this.

“We have never succeeded in establishing a link between the men and we’ve gone back years sifting through phone records, contacts and interviews,” Mr Zammit says.

Claire Zammit Xuereb – daughter of construction magnate Anġlu Xuereb and the only witness – has always maintained they did not know the intruder.

She had recounted how she woke up and found herself “in the middle of a horrific nightmare” to see her husband being fatally stabbed by “a man dressed in black”.

The Police Commissioner has personally reached the conclusion that Nicholas Gera was under some form of psychological pressure.

“Whoever you speak to who was with Gera that night will tell you he was acting uncharacteristically.

“Could it be that something made him lose his cool? Was he feeling lonely in a crowd? Had something affected him deeply when he was a young boy in Bosnia?”

Information pieced together at the time shows Duncan Zammit had spent New Year’s Eve with his wife, parents and in-laws at his home. The only time he left the apartment in Falcon House on High Street was to drive his parents to their house, a few blocks away in Tigné, around 1am.

In the meantime, Nicholas Gera was working at Shiva’s Indian restaurant in Paceville and clocked off at 3am, telling his manager he was too tired to go out.

He then drove his colleague to George Borg Olivier Street, blocks away from his own Sliema home in Blanche Huber Street.

The car he was driving, which belonged to his mother, was found parked in front of his mother’s home, a five-minute walk from the Zammits’ penthouse.

At about 4.45am he entered Muddy Waters bar in St Julian’s in a mad, uncharacteristic rage.

Some 15 minutes later he was kicked out and at around 6.30am was found dead in a pool of blood in Duncan Zammit’s apartment.

“I don’t think he intended doing what he did when he opened the door to the apartment block; he didn’t intend to kill,” the Police Commissioner says, adding toxicology results for drugs proved negative.

He also feels that by arming himself with two knives Nicholas Gera was possibly protecting himself against the unknown. If he was planning on killing it is more likely that he would have picked up one knife and left his other hand free.

The Police Commissioner thinks the unaccounted slot between 5am and 6am is the time Nicholas Gera spent roaming the penthouse – his fingerprints were found on numerous items around the house.

The police are seeking foreign experts’ help in putting together a psychological profile of Nicholas Gera

He discounts previous reports that the couple could have shared a drink with him before the stabbings – none of the glasses had Nicholas Gera’s fingerprints on them.

He also writes off the premise supported in scientific articles that multiple stab wounds in murder cases usually point to complex social relationships, while more than 20 indicate intimate relationships.

“The stab wounds indicate a frenzied attack. Frenzy is often born of a mixture of emotions... what triggered this could be a multitude of factors, the most common being passion – not only love but possibly anger, fear and sorrow – and not necessarily directed at the victim,” Mr Zammit says.

He cites the chilling Norway massacre in which Anders Behring Breivik methodically shot 69 young people gathered for a summer Labour Party camp on Utoya island.

“None of the young people killed knew Breivik or had a connection to him, but they represented the party he wanted to attack.

“This is pure conjecture, but what if as he was wandering through his flat, his anger brewing, thoughts of what he lost in Bosnia flashed through his mind, and he sought to take Duncan’s place.

“What triggered this attack? We know the door to the apartment block was faulty and once he reached the roof he found the door to the penthouse unlocked. What happened inside and why is what we’re trying to piece together.”