Ronayne Dempsey was sentenced to life imprisonment with a non-parole period of 12 years for murder.

The mood changed when Ronayne Dempsey starting yelling about his lost keys.

A rag-tag gang of associates had gathered together on a bitterly cold July night to drink at Nelson's Franklyn Village, a low-cost home to many of the city's displaced and downtrodden.

After security kicked them out of the fourth floor room shared by 17-year-old Timothy Brunsell and his half brother Tyrone Oxnan, the six person group relocated two storeys down to continue partying. All of them were under 30 and most were unemployed. Some of them had only met for the first time that night.

MARTIN DE RUYTER Timothy Brunsell has been found guilty of the manslaughter of Nelson man Bruce Mortimer.

So when Dempsey, a short, cross-eyed man with a bulldog-like expression, started berating the lanky, baby-faced teenager, calling him a "pussy", and threatening to "give him a hiding," the atmosphere became tense, Iesha Wood said.

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"When Ronayne came in he [Brunsell] stopped being his loud, happy self. I think he was scared of Ronayne," she told a jury at the High Court in Nelson last week.

That display of aggression was the first Dempsey would make on a night which culminated in the fatal beating of 45-year-old Bruce Mortimer.

On July 6 last year, two days after Mortimer's death, Dempsey and Brunsell were jointly charged with his murder. Their ten-day trial told a sordid story of poverty and violence. In the end Dempsey was found guilty of murder and Brunsell of manslaughter.

At the time of Mortimer's death Dempsey had been living on $30 a week, receiving clothes from the Salvation Army and begging his Franklyn Village "mum", Narda Thaugland, for food and cigarettes.

"I gave him whatever to help out," she told the court.

But the lure of a few hundred dollars - and a grudge against Mortimer who'd accused Dempsey of stealing his morphine a week earlier - convinced the then 27-year-old there was money to be made from jumping his neighbour.

He tried to recruit Brunsell and former village resident Eric Granger in a plan to assault Mortimer, pulling out a pocket knife and putting on what witnesses later called a "tough guy act".

"He said 'it's $200 G, it'll be easy as G," Angiata 'Arnie' Tumene said.

"He said 'If this guy doesn't give me my f***ing money I'll stab the c***'. He wasn't going to let it go that's for sure."

​Nobody wanted in on the plan. About 2am the night started winding down; Brunsell and Granger went to bed and everyone else went home.

Wood and her friend Michaela Watts were leaving Franklyn Village when they saw Dempsey and Brunsell through locked security doors standing in the corridor outside Mortimer's room.

Both women told the court they banged on the doors to get their attention but Brunsell, who had gone to Dempsey's room to return a cellphone, shooed them away.

"He put his finger up his mouth and told us to shush," Wood said.

While Dempsey's lawyers John Sandston and Michael Vesty could only argue manslaughter over murder, Brunsell's knowledge and involvement in Mortimer's assault became a sticking point throughout the trial.

Brunsell's lawyers Tony Bamford and Tagan Lyall leaned heavily on the testimony of witnesses who said the teenager "definitely did not get physical" to assert his innocence.

CCTV footage time-stamped at 2.18am on July 4 indistinctly shows a skirmish between at least two men and several village residents emerging from their rooms, roused by Dempsey yelling "you ripped me off c***".

Brunsell can be seen walking away from the savage attack which left Mortimer with a bruises, bite marks, a fractured skull and two brain haemorrhages.

Clinical psychologist Cristina Fon gave her expert opinion during the trial that Brunsell appeared "completely unaware of the gravity of the situation he was facing" when he was initially charged.

A upbringing marred by physical violence and some 30 different carers had taught Brunsell avoidant behaviours, particularly laughing at inappropriate moments.

"There was constant change, nothing consistent, nothing predictable about his environment," she said.

"He will put himself in positions where people will take advantage of him and he wouldn't realise it until after it happened."

Neither of the accused gave evidence at the trial but DVD interviews with police revealed some intentions.

As Mortimer was being flown to Wellington for emergency surgery, Dempsey conceded a history of intravenous drug use and anger issues but said he couldn't recall exact details of the assault.

"I'm trying to unravel a little bit of the negative stuff which happened in my childhood, a lot of abuse and stuff ... I want to go to Wellington to be with my son.

"In the last year and a half I've done really well but there's definitely still an angry person in there.

"All I remember is we had a fight and I'm quite shocked to hear about his injuries. Maybe I f***ing hit him too many times."

Brunsell explained how Dempsey was "intimidating" him and denied any part in Mortimer's assault.

He said he tried to "undo" Dempsey and Mortimer, to stop them hurting each other, but when he saw blood he fled.

"I could have gone to security to tell them," he told detective Kevin Hyford.

"I dunno. I didn't know what to do."

The jury deliberated for two days before returning a majority verdict on Dempsey and unanimous one for Brunsell.

​Convicted of murder and manslaughter respectively, both men will face prison time upon their sentencing in November.