It's the strawberry punnet whodunit. An entire industry was brought to its knees in September when needles were discovered in fruit picked and packed for public consumption.

Podcast Background Briefing A needle in a strawberry stack Why would someone sabotage Australia's fruit growers? It's a mystery ripe for investigation. About

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Within a week, there were reports of more than 100 incidents around Australia as well as an isolated case across the ditch in New Zealand.

Strawberries were recalled from supermarket shelves and many farmers were forced to throw away their crop.

The Federal Government responded by seeking advice on increasing the maximum penalty for food contamination to 15 years in jail — a punishment normally reserved for people convicted of child pornography and terrorism charges.

But we're still no closer to knowing who did this and why. A police investigation has so far produced no breakthroughs.

The ABC's Background Briefing program has examined the possible culprits behind the food safety scare, including the leads being pursued by officers.

The act of a disgruntled worker?

Fruit picking is gruelling work and Australia's horticulture industry relies on cheap labour.

Strawberry farmers typically employ backpackers on a seasonal basis. They help with the harvest in order to extend their visas.

But foreign workers, particularly those with limited English, also make easy targets. Allegations of exploitation and underpayment are rife.

The Fair Work Ombudsman has been running an inquiry into the issue for five years. In a landmark case, investigators successfully prosecuted Hour "George" Him, a Queensland farmer who now produces strawberries under the brand name Oasis.

Oasis strawberries are among those contaminated with needles.

Unions welcomed an inquiry into the exploitation of fruit pickers but say convictions have proven difficult to secure. ( ABC: David Lewis )

Along with a senior colleague at the time, Mr Him was convicted and fined almost $70,000 for underpaying a number of his staff at his former strawberry farm in Stanthorpe.

A fruit-picker at another farm said she understood why an aggrieved foreign worker in a similar situation might lash out.

"Maybe some packer hate their farm boss so they put the needle in the punnet," she said.

Several media outlets ran with this narrative in the days after the scandal broke.

Shane Roulstone from the Australian Workers Union recently interviewed fruit-pickers at three properties in the Sunshine State, six of whom were employed by a labour hire company.

In light of what they told him, he believes the worker exploitation motive makes sense.

"They work their workers extremely hard — 16-hour days with minimal breaks," he said of the company that recruited them.

"They feel pressured not to take comfort breaks or toilet breaks, as we'd call them."

Strawberry farmer Mandy Schultz has also heard stories about the mistreatment of backpackers in the region.

"If it was a disgruntled worker, it's probably because he wasn't treated or paid properly," she said.

"People don't go do stuff like that for nothing."

Police believe copycats are responsible for all but five of the more than 100 reports of needles in strawberries. ( Facebook: Joshua Gane )

Background Briefing can reveal Donnybrook, one of the strawberry farms at the centre of the contamination scandal, was raided by Australian Border Force (ABF) in September.

A backpacker employed there, who asked to remain anonymous, said four officers rounded up at least 35 foreign workers.

The ABF would not confirm whether employees at Donnybrook were involved but said it did raid two properties ansd two people were detained for having incorrect visas.

A spokesperson said the operation was not related to product tampering.

Police investigate why Donnybrook was targeted

The owner of Donnybrook, the strawberry farm raided by the ABF, has a colourful past.

Fairfax has revealed that Pasquale Cufari was convicted of drug trafficking in the 1990s. He also ran into trouble with the Australian Tax Office around the same time.

Donnybrook, one of the biggest strawberry producers in the Wamuran area, was targeted in the contamination scandal. ( ABC News: Mark Leonardi )

In 2003, Cufari was named in a National Crime Authority report on Italian organised crime. Specifically, he was described as an associate of a Calabrian mafia man who lives in Adelaide.

Ten years ago, his son Joe is said to have arrived in Wamuran to learn the strawberry business.

Donnybrook slowly became the region's largest producer of the fruit and it continues to expand.

Property records show the Cufaris purchased two farms in nearby Elimbah in 2016. They also bought three houses in Caboolture the same week their strawberries were recalled.

Pasquale Cufari declined to speak to Background Briefing.

In an interview with ABC Radio in Brisbane, Queensland's Police Commissioner Ian Stewart confirmed police were investigating whether there is any link between this history and their farm being targeted.

"We don't rule that out and we can never rule that out," he said.

"We are looking at all angles in this investigation."

But experts say strawberries could have been contaminated with needles at any stage of the food supply chain, whether on the farm or at the supermarkets.

The rise of so-called food terrorism

Professor Chris Elliott helped Britain strengthen its food supply after frozen meals containing horse meat were pulled from the shelves in 2013. ( Reuters: Suzanne Plunkett )

Professor Chris Elliott was in charge of investigating one of the most infamous food safety scares in recent memory.

In 2013, horse meat was discovered in products falsely advertised as beef in the UK.

Professor Elliott was part of a subsequent overhaul of Britain's food industry.

He thinks putting needles in strawberries should be regarded as a serious crime.

"I actually call that food terrorism," he said.

"One or more individuals have set out to scare people, to terrorise people."

Professor Elliott has studied parts of the food supply chain in numerous countries and says Australia stood out for all the wrong reasons.

"There isn't the level of checking and inspections that should be going on that will safeguard your food industry and safeguard all Australian consumers," he said.

"Australia was one of the countries with the highest levels of fraud that we've ever come across."

He said urgent measures were required to strengthen food security to prevent further scandals.

"I think your food industry, your government, really has to sit up and take attention."

"I can guarantee you in Australia there is a lot of fraud going [on] in your food supply system. And if you don't start to check for it, it will probably get worse."