Detective Inspector Dave Lynch fronted media outside court because the Prasad family was "too upset".
He said the two-and-a-half-year process had been extremely traumatic for them.
There were still question marks around how the victim was actually knocked out before his death and Mr Lynch said it was unfortunate the only two who knew could not be trusted to tell the truth.
"[Kumar and Permal] have simply told too many lies and will never be believed," he said.
"For family, police and everyone it's frustrating."
The victim's mother Shammi told the court the killing of her "kind and sympathetic boy" happened just four days shy of his 22nd birthday.
"How much pain must my baby have gone through? He must have cried for help and we were not there to help our baby in the final moments of his life," she said.
Mr Prasad's brother Pravin said he spent that day, which would have been his brother's birthday, on the rural roadside where his charred remains were found.
"Those images will forever be embossed on our lives," he said.
On January 30, the victim withdrew $30,050, in $100 and $50 bills, from a Manukau bank at the request of Kumar, who waited outside.
Crown prosecutor Aaron Perkins said the money element was a "significantly aggravating factor".
"Killing for financial gain is not a particularly common feature of cases in this country," he said.
Despite them both being charged with murder, Kumar was fingered as "the instigator and driving force" behind the crime.
He said on the night of January 30, Mr Prasad met the two defendants and the group drove through South Auckland.
The Crown said the victim was assaulted at an unknown location and bundled into the boot of Permal's mother's car, driven by Kumar.
The defendants then bought 15 litres of petrol, using the stolen money, before driving to McRobbie Rd in Kingseat, where they doused the victim in petrol and set him alight.
Justice Geoffrey Venning said Mr Prasad had been rendered deeply unconscious by the killers.
He said it was most likely the result of "long and deliberate compression to the neck area" and he accepted the pair probably thought he was dead at the time of the burning.
Medical witnesses gave evidence that Mr Prasad was conscious when the fire was ignited.
"The only matter of small comfort to his family may be that he was deeply unconscious at the time he was set alight," Justice Venning said.
In the days after the murder, Kumar spent thousands of dollars on his car and paying off various debts and on February 2 he and Permal went shopping together.
Store records showed they got tattoos, watches and T-shirts totalling nearly $2000.
Large sums were also deposited into bank accounts linked to Kumar.
"Money wasted on rubbish by those heartless criminals," Pravin Prasad said.
"Whatever sentence is handed down today will not be enough."
