The family of a brutally murdered teen – whose burnt body was initially mistaken by police as that of a sheep – are to present a petition to Parliament calling for better “competency” from frontline officers.

It is now eight months since Ariki Rigby was murdered in Hawke’s Bay, and her badly brutalised body was stuffed in the back of a car in a rural car park and set alight.

Her older sister Anaherā Rigby has told the Herald the 18-year-old’s hands and feet had been chopped off and she also had multiple bone breaks.

The car featuring her body had been taken to River Road Recreational Reserve late on the evening of September 2, or on the morning of September 3, and then set alight.

Police attended on the morning of September 3, mistook the charred remains for those of a sheep and a tow truck was booked to take the wreck to a crushing yard two days later.

Next month Anaherā will present a petition calling for “competent investigations for incompetent policing” to Parliament, with the petition being sparked by the mistake officers who initially visited the scene made.

She said that if it wasn’t for a dog walker - Hastings man Kevin Monrad who realised the body had shoulder-length hair and was wearing a necklace - they would never have recovered Ariki’s body.

Police officers scour the area near where the torched car containing Ariki Rigby's was found in a rural car park last September. Photo / Neil Reid

“It is more saddening than frustrating,” Anaherā told the Herald.

“My sister had gone through something so brutal, and she could have been back with her family earlier. For two days, she was on her own lying there.

“And we only just got her body back . . . barely.

“If he [Monrad] didn’t find her in time, the car was going to get towed and crushed. She would forever be a missing person.”

The car was set to be picked up the day Monrad made the grisly find.

Anaherā has previously said her sister was slain by several gang-affiliated people, adding she believed the motive was down to “jealousy and drugs”.

Anaherā said she believed the way the first officers neglected to realise the body stuffed in the back of a car was human was incompetent.

The fact Ariki’s remains lay in the car for a further 48 hours increased the trauma experienced by the teen’s loved ones.

The family of Ariki Rigby have united with that of missing woman Breanna Muriwai, pictured, in a bid to raise awareness of the two cases, and other unsolved crimes. Photo / Supplied

That, plus hearing of the experiences of other families of unsolved cases – including that of missing woman Breanna Muriwai, last seen on the Kāpiti Coast in August – had seen Anaherā start a petition calling for better reviews of cases where police had made mistakes, or which remained unsolved after a lengthy time.

“We need competent investigations for incompetent policing,” she said.

“I am trying to do this for everyone so it doesn’t happen again.”

Anaherā said her heart went out to the loved ones of Muriwai, who believe she was murdered and also believe they know who did it. She said they had no form of “closure” while her body has not been recovered.

“We do [have some closure], just barely and by luck,” she said.

Anahera Rigby, pictured along with cousin Michael Ngahuka, continues to urge those with information about her sister's murder to come forward. Photo / Supplied

“That is why I am trying to help out her family a lot.”

Anaherā was also now a member of the Unite as One, Unite for All group; a movement set up by Muriwai’s mother which offers support to families of missing people, as well as those impacted by unsolved crimes and serious crime.

On June 1 the group will lead a New Zealand Justice march raising awareness for missing people and unresolved cases from Wellington’s Civic Square to Parliament. The petition will be presented to MPs at the end of the march.

Detective Inspector David de Lange said police realised “this had been an extremely upsetting time for Ariki’s family”.

Police were committed to “holding the person or persons responsible” for her death to account.

Eight months on from Ariki Rigby's brutal death, friends and loved ones gather at the spot where her body was found in a burnt-out car at River Road Recreational Reserve, Havelock North. Photo / Neil Reid

“At the moment our focus remains on the active investigation into Ariki’s death. This includes analysis of all evidence to date,” de Lange said.

“We reiterate that the investigation remains at a sensitive stage and we are continuing to make progress.”

He added that a review of the initial police response would be carried out “as part of the debrief, following the conclusion of the criminal investigation.

“Any review of an investigation is an important part of identifying opportunities for improvement and lessons learnt.”

Police continue to urge anyone with information “to do the right thing” and get in touch with Police via 105, quoting file 220905/1265.

Information can also be provided via Crime Stoppers anonymously on 0800 555 111.