As he lay on the side of the road with blows raining down on him, the experienced highway patrol officer thought he would die and could only hope his training would get him through it.
Snr Const Mellor had just stopped a Mazda that was being driven erratically near Taihape on Saturday morning and had no idea anything was wrong as he walked back to his patrol car to check the teenage occupants' details.
"He didn't see it coming. He had no inkling at all," said Police Minister Judith Collins after visiting the injured officer in hospital yesterday.
"It was a frenzied attack and he has sickening injuries. I've never seen so many staples in one place; it's unbelievable."
The attack was so vicious Snr Const Mellor's's cellphone, which was tucked into the top of his stabproof vest, was sliced along with many other parts of his body.
A passing motorist found him lying in a pool of blood and he was rushed to Palmerston North Hospital with multiple skull fractures, broken teeth, a broken eye socket, a broken jaw, cut arms and a damaged finger.
Yesterday, Snr Const Mellor's eyes were almost swollen shut.
But, despite suffering what were initially feared to be life-threatening injuries, he was in a stable condition last night and even "cracking a few jokes", colleagues said.
"He's in pretty good spirits but he's still not out of the woods," said Detective Inspector Chris Bensemann.
"They are still monitoring the brain bleed every four hours."
Det Insp Bensemann said the two teens, who fled after the attack, crashed nearby and were arrested.
An 18-year-old has been charged with unlawfully taking the car, attempted arson of it and assault. A 14-year-old, who is now in CYF custody, is charged with unlawfully getting into the car, attempted arson and assault. Further charges are being considered and both are due to appear in the Wanganui District Court today.
Det Insp Bensemann said Snr Const Mellor seemed like he "just wants to get back on the horse".
Waiouru-based Snr Const Mellor mainly works between Taihape and Waiouru and police say it was not unusual for him to be working on his own when the attack happened.
He has been in the job for 35 years, first with the Ministry of Transport, then with the police, but this is the first time he has been injured.
Snr Const Mellor told Ms Collins his training in knowing to roll into a ball had probably saved his life.
Local people where Mr Mellor works have described him as "one of the best country cops in the country".
The attack has reignited the debate about whether police officers, especially those on the front line, should be armed.
Police Association president Greg O'Connor said the time had come to carry firearms.
Police Commissioner Howard Broad is due to meet the minister today to present the findings of a report commissioned after two police officers were shot in Christchurch earlier this year.
Ms Collins is expected to comment further once she has seen the report.
