Adelaide lawyer Stephen McNamara alleged to have stolen $850,000 from two dead people

An Adelaide lawyer defrauded $850,000 from two deceased estates by fabricating investments on their behalf, a court has heard.

Stephen McNamara is on trial in the South Australian District Court charged with multiple counts of theft, aggravated theft and using fabricated evidence between 2011 and 2013.

In opening the trial this morning, prosecutor James Slocombe told the jury McNamara had abused the trust placed in him as executor of the two estates.

"Instead of honestly and diligently holding on to the estate funds like he was supposed to, he took the money to be used for his own purposes," Mr Slocombe said.

He said the "sophisticated and dishonest" system involved making fake investments in companies.

"He was moving the money out of the sham investment account into a number of other bank accounts," he told the court.

"It was then ultimately used to pay for personal expenses like his mortgage repayments, outstanding wages owed to his law firm's staff and for other personal expenses."

Craig Caldicott, for McNamara, said the jury would have to decide whether McNamara took the funds for his own use.

He said lawyers' trust accounts do not earn any interest, and there is sometimes an obligation on lawyers to invest the money if it is in the trust for an extended period.

A second man, Philip John Pitman, is also on trial, charged with one count of using fabricated evidence as he allegedly assisted McNamara.

Several lawyers, a forensic accountant, a beneficiary and a detective are expected to be among those who give evidence during the two-week long trial.