It was one of the biggest gun-smuggling operations in Australian history — a brazen scheme that shocked New South Wales Police and embarrassed Australian Customs officials.

A syndicate working out of a suburban Sydney post office smuggled more than 130 high-powered, highly restricted semi-automatic handguns into Australia through the mail, at a time when the city was in the grip of an outbreak of drive-by shootings.

At the time of their arrest in 2012, the syndicate had plans to bring in hundreds more Glock pistols into Australia.

Only a fraction of the handguns they smuggled in have ever been found. More than 100 are still on the streets, in the hands of criminals.

"It's a well sought-after gun, a Glock pistol. It's not dissimilar to a sports motor vehicle. It's something that everyone would like to possess. The Glock pistol is like a Ferrari of handguns." — Detective Chief Insp. Grant Taylor, NSW Police Firearms Squad, 2009-2012.

For five years, the ringleader of the syndicate has dragged his case through the courts. Only now can the full details be revealed of a scheme that firearms experts have told Four Corners is a "wake-up call" for Australian authorities.

January 2012: A shot in the night puts detectives on the trail

"How can a large number of Glock semi-automatic pistols … end up in Australia, and all of a sudden end up in the Western Suburbs of Sydney? That's the wake-up call." — Gary Fleetwood, Australian Criminal Intelligence Commission.

The operation only came to light after a reckless gunshot by a low-level criminal on the streets of Sydney, that put investigators on a trail that led to gun dealers in Germany, Switzerland, and the United States — and back to a suburban post office in Sydney.

In the early hours of morning, in the Sydney suburb of Wiley Park, a couple are loudly arguing in their car.

When a nearby resident tells them to shut up, he is shot at.

Police chase the vehicle, and search it. This police video records the discovery of a pistol on the floor of the car.

Sorry, this video has expired Glock found after police chase

"I've removed one bullet from the chamber. OK, the weapon is now clear." — police officer.

The gun is an immediate red flag. It's a Baby Glock semi-automatic pistol — easily concealed, and available only to law enforcement officers in Australia.

Grant Taylor: "The Glock is like the Ferrari of handguns". ( ABC News )

But police also notice that the serial numbers on its three major parts don't match — and that all its components are virtually brand new.

Police realise they are now investigating an international smuggling operation.

"When there's smoke, there's fire. And if someone has got in three, there's a high possibility that there's more. So that pretty well launched Strike Force Maxworthy." — Det. Chief Insp. Grant Taylor

February 2012: 'There's a market out there … we are the providers'

Maxworthy detectives contact the Glock factory in Austria and learn that the weapons were sold to a small gun dealer in Germany, who in turn sold them to a buyer in Australia.

The guns were delivered to a post office in suburban Sydney.

The owner of the post office franchise, Andrew Botros, is known to police. He is placed under surveillance and his phones are tapped.

So are two other suspects. One is Ahmed Karnib, who works at a nearby freight forwarding company. The other is Optus technician Khoder El Ali — the man police identify as the ringleader of the scheme.

Police listen in as the men use their own crude code to discuss gun shipments.

Sorry, this video has expired Ahmed Karnib and Khoder El Ali talk about 'fishing reels'. Warning: Contains strong language

Ahmed Karnib: "How much stock are we talking about?" Khoder El Ali: "They're looking at getting us at least 80 fishing reels." Karnib: "Eighty fishing reels, that's pretty good." El Ali: "Cuz, let's do it bro. All these f***in' tackle shops mate, they'll buy this stuff straight away. It's a big market, in the fishing industry mate. No f***in' around." Karnib: "Like we said, there's a market out there and we, we are the providers." El Ali: "That's exactly right. I'll talk to you soon buddy."

When the gun dealer in Germany is also placed under surveillance, police discover that another consignment of gun components is already on its way to Australia.

When the package arrives, this time Customs officers are waiting. Inside the box they find 140 Glock pistol magazines.

Detectives believed the discovery of 140 Glock magazines meant there were 140 Glock pistols heading for the streets. ( Supplied )

Police immediately realise the scale of the smuggling scheme.

"We had to act quickly. If someone had asked for 140 magazines, we knew that somewhere there would have been 140 Glock pistols. But we weren't sure if they were still in Germany, or in Australia — and we certainly didn't want any more Glock pistols entering Australia." — Detective Sergeant Fab Furia, NSW Police Firearms Squad

Firearms squad detective Fab Furia: "We had to act quickly" ( ABC News )

March 2012: The sting … and the arrest

Police decide to set a trap, using the seized package with the Glock magazines.

The box is repacked and fitted with a listening device. It's then delivered to the post office by an undercover Customs officer posing as a courier.

Sorry, this video has expired Customs officer delivers gun parts to Botros's post office

'They were able to tell us that they knew that inside that package was parts for a Glock pistol and in particular the magazines. It worked perfectly.'

— Det. Chief Insp. Grant Taylor

After the package is delivered, Botros and Karnib are recorded discussing the package — and the pistol magazines it is supposed to contain.

Sorry, this video has expired Botros and Karnib discuss the intercepted shipment

Andrew Botros: I can't believe it. Is it only mags in it?

Ahmed Karnib: Yeah.

Unidentified male: For what? For nines? For fives?

Karnib: I don't know what size. It's for the Glocks.

Botros: Oh, for the Glocks. For the nines.

Botros is arrested in the post office, but denies any knowledge of the package.

Karnib is arrested at the nearby shipping office where he is employed. He also maintains his innocence — even claiming to have met one of the false identities used by El Ali to buy guns online.

El Ali is arrested while driving with his wife.

"Amazingly, they were still arrogant to the last moment and beyond. I think they believed that this just wasn't happening when they were arrested, and that we would never be able to formulate a case against them." — Det. Chief Inspector Grant Taylor

Sorry, this video has expired Police move in to arrest Andrew Botros

Police officer: Can you tell me anything about that box? Botros: No. They shouldn't even be delivering that box here. That's Fedex. Police officer: Do you know what's in the box? Botros: No I don't. Not at all. I haven't signed for that.

More than 100 guns still unaccounted for

Of the 132 pistols smuggled in, police have recovered just 24. They've been found on bikies, at meth labs, and on Middle Eastern crime gang members.

One was even found hidden in a giant teddy bear.

Sorry, this video has expired Police raided this suspected gang member's home — and found a Glock hidden in a giant teddy bear. Warning: Contains strong language

Botros and Karnib later pleaded guilty to importing prohibited goods and selling firearms parts.

Karnib served almost four years in prison; Botros spent less than two years in custody until he was bailed and placed on a good behaviour bond.

El Ali was convicted of conspiracy to import the guns, as well as possessing and supplying them.

He was sentenced to a minimum of 13 years, and will be eligible for parole in 2025.

Watch the full Four Corners episode on ABC iview.