"We appeal to witnesses in either Seddon St or Clelend Cres to come forward and let us know what happened. Somebody amongst that group will know what's gone on.
"We know there's been an incident in Celeland Cres outside the party when a car has arrived there. We want to know what's happened there and around the corner on Seddon St."
Mr Barnett thought the car in question had arrived to pick people up.
Mr Whanga-Elliott was found just before 3.30am but police inquiries were also focusing on when he was assaulted.
Police believe about 30 to 50 people were at the 21st at which Mr Whanga-Elliott died and are appealing for witnesses to the attack or those who attended the party to come forward. He understood there were family members and friends of Mr Whanga-Elliott present.
"The appeal is for them to come forward. They know what's happened."
Talosage Terry David Moreli has been remanded in custody after appearing in the Hutt Valley District Court charged with assaulting the man and a separate charge of assaulting another man.
Police were now treating the death as a homicide and were working to piece together what happened.
At this stage, no more charges would be laid against other party-goers as officers looked into what had gone on at the house. It was too early to make any final decisions though.
A post-mortem took place this morning and police are waiting the pathologist's report for a definite cause of death.
A grieving family member has expressed his outrage over losing Mr Whanga-Elliott at what should have been a peaceful family celebration.
The relative, who posted a photo of Mr Whanga-Elliott on life support, asked what happened to warrant the 21-year-old being attacked after being specially invited to join the party.
"Get your boy to come around, invite [Mr Whanga-Elliott] over to your boy's 21st so you could take [his] life."
The man said those who once called themselves family could "kiss all that goodbye".
He described the pain of Mr Whanga-Elliott's passing as ripping the biggest hole in his chest.
"This s*** is gonna take me a long time to heal from this and in all honesty I'm never gonna forgive you for taking [Mr Whanga-Elliott] from me ever."
The dead man's cousin Kahu Walker posted an heartfelt tribute soon after his death.
"Rest easy," she posted.
"You're finally free," she wrote. "No more worries, no more pain. You're in God's arms now look over us aye."
"See you soon my cousin. Until we meet again."
She also sent a warning that the 17 people responsible would be brought to justice.
Friend Phoenix Fetoai asked: "When does this end? Rest in love Jardin."
The slain 21-year-old's rugby league club today paid tribute to a talented player who joined as a teenager and played top-level age-grade competition.
Petone Rugby League Club chairman Thomas Meihana said everyone at the close-knit Wellington club was "deeply saddened by the loss of one of our own".
His grandparents Eddie and Cory Elliot were life members of the club and Jordan had joined as a teen, playing in the U17 premier grade.
"He was a good player and always willing to help out around the club with his family," said Mr Meihana.
"Jardin will be sadly missed by the club and his old team mates."
Mr Meihana said the club would focus on supporting Jardin's family at this difficult time.
"Our sincere condolences go out to his entire whanau.
"Moe moe ra e Tama."
Cleland Cres was quiet today, but neighbours said the house that hosted the party was often noisy.
One man had previously heard party-goers running down the road shouting "die, die, die". He slept through Saturday night's party but thought he might have heard shouting on the street at some stage.
"There's always been parties there," he said.
There is no police presence at the house this morning but officers and security guards were around until yesterday.
The man said what happened was "quite shocking" in a street that could be loud.
"I heard partying last night but I'm not sure if it was coming from there."
Further along the street a man said fighting broke out outside his house.
A woman he lived with called police but it moved on.
