The former public officer of Australia's oldest and richest Aboriginal land trust has pleaded guilty to stealing close to $500,000 from the beneficiaries of the trust, while another $33.5 million of trust funds remain unaccounted for.

Key points: The guilty plea related to theft of property from Groote Eylandt Aboriginal Trust beneficiaries

The guilty plea related to theft of property from Groote Eylandt Aboriginal Trust beneficiaries The money was spent on vehicles, boats, quad bikes, and cash payments to a friend

The money was spent on vehicles, boats, quad bikes, and cash payments to a friend Ms Lalara's sentence is expected to be handed down next week

Rosalie Lalara, 59, pleaded guilty in the Northern Territory Supreme Court to stealing property from the beneficiaries of the Groote Eylandt Aboriginal Trust (GEAT) to the value of $475,000 in the space of approximately 12 months beginning in June 2011.

Agreed facts read to the court on Tuesday revealed Ms Lalara, who was the public officer of GEAT from 2011 to 2013, spent the trust money on multiple four-wheel drives, boats, quad bikes and trailers.

There were also cash payments to a close friend, Ben Tamwoy, who was not a beneficiary of GEAT and so was not entitled to benefit from the Trust's money.

The agreed facts detailed eight trips Ms Lalara and Mr Tamwoy made to car and boat yards in Cairns and Darwin between 2011 and 2012 where Ms Lalara purchased up to 15 boats at a time with trust money.

While the majority of boats made their way to beneficiaries on Groote and Bickerton islands, in total 12 vehicles bought by Ms Lalara were given to Mr Tamwoy or his friends based in Queensland, none of whom were beneficiaries of GEAT.

Prosecutor Damien Jones told the court on Tuesday, Ms Lalara's motivation for stealing from the trust was "purely personal … that is to ingratiate yourself with Mr Tamwoy and his family".

"She is bestowing him with lavish gifts — boats, cars, quad bikes," Mr Jones said.

He added even a rugby league club he was "sort of associated with", the Injinoo Crocs, was given $14,000.

In April 2012, Ms Lalara bought 11 boats at a total cost of about $429,000.

The largest of these, a Surtees Silver Bullet worth $79,000 and a dinghy valued at $35,000, were given to Mr Tamwoy.

The other nine boats purchased by Ms Lalara were never collected.

Ms Lalara's lawyer Marty Aust pointed out $400,000 worth of goods bought by Ms Lalara had been reclaimed by GEAT's lawyers and police, although their resale raised just $67,800, according to court documents.

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The lawyer said Mr Tamwoy had told Ms Lalara he would come to Groote and act as role model to young men in the community.

Mr Aust claimed there was "never a romantic relationship" between Ms Lalara and Mr Tamwoy.

He said when "angry mobs turned up at her house screaming and chanting and wanting her blood", Ms Lalara turned to Mr Tamwoy for support.

The ABC reported in November 2015 that $34 million of GEAT money was spent between 2011 and 2013.

Much of this was spent on beneficiaries of GEAT but poor record-keeping means there is little evidence of exactly where and to whom the money went.

What is GEAT and why is it so rich?

In the 1960s the traditional Aboriginal owners of Groote and Bickerton islands, off the coast of Arnhem Land, signed a royalty agreement with mining company BHP.

It was the first agreement of its kind in Australia between Aboriginal people and a mining company.

Groote Eylandt's manganese mine — now owned by South32, a subsidiary of BHP — pays tens of millions of dollars a year in royalties to the beneficiaries of GEAT.

Groote and Bickerton islands often appear in lists of the richest postcodes in Australia.

The small population of the two islands and large royalty payments over 50 years make the Aboriginal beneficiaries of GEAT wealthy individuals, on paper.

But despite the hundreds of millions of dollars paid into GEAT for the benefit of the community, education and health outcomes on the islands remain poor.

The prosecution submitted a victim impact statement on behalf of "beneficiaries of GEAT", written by Elvis Barra, which described the mistrust.

"Rosalie Lalara is my granddaughter. When she was running the trust I knew I could not trust her. She has taken too much money away from these poor communities," the statement said.

"We would share everything on Groote but now people don't trust each other.

"She has hurt the community … now we do not know who to trust."

It was revealed in court on Tuesday that $15,000 of GEAT money that should have been spent on its beneficiaries was instead pledged to local football club the Injinoo Crocs, in Queensland, by Ms Lalara.

Her close friend Mr Tamwoy, the beneficiary of much of Ms Lalara's admitted theft, is a former player for the Injinoo Crocs.

Another $18,000 was withdrawn as cash from GEAT accounts and given to Mr Tamwoy by Ms Lalara.

The former GEAT public officer told KPMG — the trust's long-term accountants — the money was for funeral costs and ceremonies in the community.

End of a long-running saga

Ms Lalara first appeared in court accused of stealing from GEAT in 2013.

There have been many dramatic moments in her case since. In late 2015, representatives of the Original Sovereign Tribal Federation (OSTF), a group that challenges the Commonwealth's legal jurisdiction over Aboriginal people, approached Ms Lalara advising her to reject the validity of the Northern Territory's Supreme Court to hear her case.

A member of OSTF accused the presiding judge, Justice Graham Hiley, of treason from the public gallery.

Ms Lalara subsequently sacked her legal representatives twice in 2015, once just moments before agreed facts were tendered to the court in December 2015.

Ms Lalara was not accompanied by any members of her family or supporters from OSTF in court on Tuesday.

Her lawyer requested Justice Hiley give his client a partially suspended sentence, citing her poor health, her status as a first-time offender and her need to care for a disabled daughter as reasons to minimise her time in prison.

Ms Lalara's sentence is expected to be handed down next week.