A “substantial” land search is under way for Waikato mother-of-three Sara Niethe.

Her body has never been found despite her boyfriend Mark Pakenham admitting he killed her.

Niethe was last seen in Ngatea, on the Hauraki Plains, on March 30, 2003.

Pakenham was charged with her murder in 2011 but before his case went to trial he pleaded guilty to a reduced charge of manslaughter.

He has always refused to tell police where Niethe’s body is, but admitted he injected Niethe with methamphetamine on March 30, 2003, causing her death.

Mark Pakenham admitted killing his girlfriend Sara Niethe on or about March 30, 2003 at his Kaihere home. Photo / Sarah Ivey

Pakenham was sentenced to six years and seven months in prison and refused parole repeatedly until he was finally released in 2016.

The Herald has learned that Niethe’s family have now commissioned a new search for her body.

A team is currently working in an area at Kaihere, a small rural settlement that overlooks the Hauraki Plains.

It is near where Niethe was last seen at Pakenham’s home.

The search is being run by a private investigator on behalf of Niethe’s family.

The Herald has contacted the investigator for more details about the search, which has been described as covering a “substantial” area.

Mark Pakenham admitted injecting a large dose of methamphetamine into Sara Niethe. File Photo / Greg Bowker

The search is being carried out by Land Search and Rescue and volunteers. Police are not involved.

When Pakenham was sentenced for Niethe’s manslaughter, the court heard details of her last hours.

On the day she died, Niethe went to Pakenham’s house and the couple drank bourbon, smoked cannabis, and had sex.

Pakenham later told police the couple had an argument and Niethe left in her mother’s car.

But it later emerged Pakenham injected Niethe with the then class B drug methamphetamine.

In recordings police took of Pakenham talking to an associate in 2009, he admitted to giving Niethe a “shot of meth”.

 “She’d never been blasted before and it f*#ked her,” Pakenham was recorded saying.

He told the friend Niethe’s death was not “a nice way to go” after she began squirming.

He only admitted the situation once police played him the recordings in 2011.

Justice Timothy Brewers denounced Pakenham’s decision to not help Niethe and it would never be known if he could have saved her life.

“You saw her die and did nothing to help her.”

Justice Brewers also denounced Pakenham’s violent offending against women and the fact he continues to “conceal” the body and the car.

The judge said he accepted Pakenham was under the influence of drugs and in shock when he hid Niethe’s body - but noted Pakenham composed himself enough to return her sunglasses, phone and cigarettes to Niethe’s youngest daughter the next day.

“You still did not tell the family or the authorities.”