An Adelaide lawyer has been found guilty of stealing $850,000 from two deceased estates and fabricating documents claiming the money had been invested in Australian opal in order to cover his tracks.

Key points: Stephen Patrick McNamara was the architect of an elaborate scam involving two deceased estates

Stephen Patrick McNamara was the architect of an elaborate scam involving two deceased estates The lawyer claimed money was being invested in opal, but it was instead used to pay off his mortgage and wages

The lawyer claimed money was being invested in opal, but it was instead used to pay off his mortgage and wages His associate was found not guilty, with a judge finding he could have been a "puppet"

District Court judge Michael Boylan found Stephen Patrick McNamara — who has been a lawyer for more than 35 years — guilty of 33 charges of theft and fabricating evidence in court proceedings.

His associate, Philip John Pitman, was acquitted of one count of using fabricated evidence in a judicial proceeding.

Judge Boylan found parts of McNamara's evidence to be "implausible".

In his judgement, he said the case had an "unfortunate history" after two previous trials by jury miscarried.

McNamara was the director of his law firm Commercial and General Law, and Mr Pitman was a trustee of the Andamooka Opal Stone Unit Trust (AOSUT), which owns a large quantity of Australian opal valued at almost $300 million.

Over an 18-month period, McNamara drained funds from the first estate, worth $480,000, and used the money to pay off his mortgage, personal credit cards and staff wages.

Judge Boylan said pressure from the four beneficiaries — the children of the deceased — to get their entitlements then started to mount.

"Because he had exhausted the estate funds in that way, McNamara was unable to distribute the estate among the beneficiaries," he said.

He then siphoned money from a second estate, worth $500,000, to pay the beneficiaries of the first estate he had stolen from.

It was the beneficiaries of the second estate who made a complaint to the Law Society of South Australia, which triggered an investigation.

"As a result of their complaint, the Law Society decided to appoint a supervisor to McNamara's trust account," Judge Boylan said.

"In an attempt to prevent the appointment, McNamara issued injunctive proceedings in the Supreme Court."

As part of those proceedings, McNamara and Mr Pitman provided signed affidavits and a letter to the court stating the estate funds had been invested.

"The prosecution case is that, having stolen the estates' funds from his trust account, Mr McNamara tried to cover his tracks by pretending to have invested those funds in AOSUT," Judge Boylan said.

Associate may have been a 'puppet'

Prosecutors relied on a series of Skype and text messages, emails and letters found on McNamara's phone and computer to argue that he, Mr Pitman and other AOSUT associates "were engaged in creating a false set of records to hide McNamara's thefts".

In one message to the AOSUT secretary, McNamara said: "Anyway what will stop all this is money coming from the Andamooka Opal Stone Unit Trust. In the first instance the $460K is needed".

"If the trust can arrange this in any way it would certainly diffuse the pressure. The solution is money. In the scheme of things, it is not a large amount. It just has to be raised," McNamara said.

Judge Boylan found no money from either estate had been invested with AOSUT.

"I find that he stole $385,000 from the [first] estate and $465,000 from the [second] estate," he said.

But Judge Boylan said he was not satisfied beyond a reasonable doubt that Mr Pitman knew the money had not been invested with AOSUT.

He said it was possible Mr Pitman was used as a "puppet".

McNamara will be sentenced at a later date.