Sam Melkie.

Sam Melkie.

An armed robber serving time for an armoured van heist that saw a security guard gunned down outside a south-side club has been caught with drugs in his sock.

Sam John Melkie, who is doing a nine-year stretch for aggravated robbery, has to serve at least four years before he is eligible for parole.

The 54-year-old serial criminal, with a 30-year history of drug abuse, was last year jailed for his part in the high-profile 2004 armed hold-up outside the Mawson Club.

Melkie and a co-offender robbed a cash transit van outside the club in broad daylight, making off with more than $150,000.

It was alleged his partner-in-crime fired a shotgun which struck one of the guards in the face. The guard survived the shooting.

A second man pleaded not guilty to taking part in the robbery and is due to stand trial in the Supreme Court.

Melkie pleaded guilty and told police he took part in the robbery because he believed he was in debt to his employer after buying drugs from him.

In February last year, now retired Supreme Court judge Malcolm Gray ordered Melkie be kept in custody until at least August 2015.

He set a short non-parole period because Melkie had turned his life around and lived crime free for several years. At the time the robber was also caring for his wheelchair-bound wife, whose predicament the judge said invited ''considerable sympathy''.

But Melkie was back in court on Monday, pleading guilty to cannabis possession after being caught with 4.5 grams in his sock.

Guards became suspicious after noticing a bulge in his sock during a visit from family members, including his wife, Marilyn Anderson.

A custodial officer challenged Melkie, who removed his shoe to reveal a balloon in his shoe.

When asked what was in the balloon the prisoner replied, ''probably dope, I'm not sure''.

The guard said, ''you're a fool, who gave it to you'', to which Melkie replied, ''one of my kids''.

Melkie's visitors denied any knowledge of how the drugs got into the sock.

Melkie pleaded guilty to possessing less than 25 grams of cannabis, a charge carrying a maximum penalty of $110 fine.

Melkie told Magistrate David Mossop he was already reprimanded under the prison disciplinary system, but the magistrate said he was unable to take that into account. He fined Melkie $80 which, along with court costs, leaves him liable for $209.