On Tuesday, Arnautovic, 55, was found guilty in the Melbourne County Court of the commercial supply of heroin and trafficking of methamphetamine, also known as ice.

The trial was told police had been watching Arnautovic for months, even involving undercover police to pose as his buyers in three covert "buys" as they built their case.

In the world of crime, a moniker tells you more about the character of a crook than his criminal record or the tattoos down his arm and Arnautovic had earned the title Machine Gun Charlie, for his rat-a-tat style in the boxing and kickboxing rings.

Arnautovic was a national kickboxing champion and the owner of a gym in Melton West and, as police put it, one of the state's most prolific heroin dealers.

He'd been dealing heroin between Melbourne and Geelong since the 1980s, and by 1999 he'd done time in jail.

Trusting very few people and preferring to operate alone, when Charlie was caught he would learn from his mistakes and regroup.

As he smartened up his game he hid his stockpile in public places, with some buried under football fields, parks and public buildings across Melbourne's western suburbs.

One of his early hiding spots was in a dead end street in Sunshine, another was the Altona North Baseball Centre where police found heroin stashed in Berocca containers and stuffed in the gaps in the walls.

Arnautovic was always tough – in one of his final boxing matches he fought on for several rounds with a broken arm, much to the delight of his fans.

And as his reputation in the ring grew, so too did his association with figures in Melbourne's underworld.

When gangster Willie Thompson was gunned down, execution style, in Chadstone in 2003, after leaving a training session at a martial arts club, Arnautovic signed a newspaper tribute to him, reflecting on the "many great times in our early days".

"I will never forget the hard spars at Bob Jones, even though we drifted apart, and went our separate ways – those memories will stay with me forever," he wrote.

Between 1999 and 2012, Arnautovic did three stints behind bars. By 2016 he was back on police radar, dealing again.

Arnautovic was put under 24-hour surveillance and, unbeknown to him, he'd been selling to covert cops. The pivotal phone call with his mother in December 2016 came three months into the Victoria Police sting, dubbed Operation Rehangs, led by Geelong drug squad's Senior Constable Daniel Hughes and his regional team.

Police were preparing to arrest Arnautovic on the morning of December 17, when one police colleague deciphered the phone call about the Telstra man. It was "pot luck", as one officer put it.

(Arnautovic and his mother largely speak with each other in Croatian but fortunately for Geelong police an officer in the drug squad also speaks the language.)

It was enough to convince police that Arnautovic's honey pot was hidden beneath his mother's home and at the last minute they added her St Albans address to their search warrant.

The move was highly lucrative.

In a hole under his mother's place police found his haul – 502 grams of heroin and 55 grams of ice in ziplock bags within two plastic containers.

His mother hasn't been charged.

Arnautovic's escapades came to an end when police arrested him in the car park of a Geelong motel, a far cry from the spotlight of the international boxing rings he once graced.

The 55-year-old was found guilty this week by a County Court jury of trafficking a commercial quantity of drugs.

He will be sentenced at a later date.