A financial adviser who "preyed" on vulnerable retirees to swindle their life savings — worth millions of dollars — has been jailed for at least seven years, with the judge describing his offending as "cruel".

Key points: Judge Michael Boylan said Gibbs admitted he stole from the easiest targets

Judge Michael Boylan said Gibbs admitted he stole from the easiest targets Gibbs had complete control over the finances of some of his clients

Gibbs had complete control over the finances of some of his clients Victim Helen Cocks said Gibbs left her with $1,000

James David Gibbs, 51, pleaded guilty to multiple theft and dishonesty charges.

South Australia's District Court heard he systematically stole money from 30 of his clients, totalling $4.8 million.

In his sentencing, Judge Michael Boylan said Gibbs had cruelly preyed on his most vulnerable clients.

"Having heard the impact statements of your various victims I think it is correct to describe your offending as cruel," Judge Boylan said.

"Many of them were retirees or preparing for retirement, they had worked hard and saved throughout their working lives in the hope of enjoying a comfortable retirement.

"As you admitted yourself, you stole from the easiest targets, your clients who had placed their blind faith and trust in you.

"You have caused great suffering to many people."

Court found Gibbs had known his victims for years

Judge Boylan said many of the victims had known Gibbs for years and he had gained their trust.

"Your clients, now your victims, trusted you to manage their financial affairs, you repaid their trust by stealing their money and spending it for your own purposes," Judge Boylan said.

Today Tonight Adelaide tracked James David Gibbs down in Alice Springs in 2016. ( Today Tonight Adelaide )

The court heard Gibbs had control over some of his clients' share portfolios and bank accounts.

"In some cases, you had near complete control over their affairs," Judge Boylan said.

"They trusted you completely, some of them regarded you as a close friend, a number of them relied on your advice without question, all the while you were systematically stealing their life savings from them."

The court heard Gibbs had low self-esteem and had begun offending to "save face" in the wake of the global financial crisis.

It heard over the course of the offending Gibbs had transferred some money back into his victims' accounts, making the net loss to his clients about $3.5 million.

After allowing a substantial discount for Gibbs's guilty pleas, Judge Boylan sentenced him to 10 years in jail with a non-parole period of seven years.

'He took everything we had', victims devastated by fraud

Outside court, many of the victims expressed their disappointment with the sentence and detailed the devastating impact of his crimes.

"It's not enough for what he's done to people," one victim, Helen Cocks, said.

"We were devastated because he just took everything that we had, I think he left us with about $1,000."

Ms Cocks said Gibbs had stolen everything from her and her husband, including both of their superannuation balances and an inheritance they received from her mother-in-law.

"We were just dumbfounded, we just couldn't believe that he would do that to people because we'd known him for so long," she said.

"Most of the [victims] have got a lifetime of hurt and trying to cope with depression and everything else."

Another victim, Enver Shabanay, said he lost both his houses as a result of the offending.

"We trusted him … it's devastating. He has destroyed my life," he said.

Former worker describes offending as 'appalling'

A former employee of Gibbs, Paul Bayly, said he also felt shocked and betrayed.

"To see the hurt that they suffered it's just atrocious, to see the stress that they've been under and financial issues, it's just appalling," he said.

"I thought he was a nice bloke, like a lot of people did.

"He duped me, he duped a lot of people, unfortunately they have suffered immensely."

In a statement on its website, the Australian Securities and Investments Commission (ASIC) said clients should always have access to information about their own investments.

"Clients need to be able to trust their financial advisers, and in this case, Mr Gibbs breached that trust," ASIC commissioner Danielle Press said.

"ASIC's investigation revealed that Mr Gibbs deliberately withheld information from clients to avoid detection.

"Financial advisers should always allow clients to access information about their own investments, and clients should be concerned if this is not occurring."