Police will allege in court that the man was operating as an online vendor on the dark web, selling prohibited drugs and prescription medications, and was assisted by the women to package and post the items to buyers across Australia.

Maybe it was because the detective, a Serbian refugee, had overcome many obstacles in his life that he readily took on the seemingly impossible case without looking for a way out. When you grow up with a minefield at the end of your street, you tend to develop a healthy level of resistance to adversity.

The death he was asked to investigate was interstate and the trail to Victoria, where he was based, was tenuous at best. The file contained a few screenshots from the computer of a young man who had died of an overdose in Perth. Worse still, the trail disappeared into the Dark Web, the internet's version of quicksand.

But Senior Detective Igor Rusmir was prepared to have a go, even though he admits “I felt totally out of my depth”.

The brother of the 25-year-old victim had found his computer password, which showed Dark Web transactions purchased with Bitcoin.

Henry Phillips, a graduate of Perth’s Scotch College and the University of Western Australia, was, according to his brother Ryan, hiding anxiety issues beneath a happy-go-lucky facade.

Henry Phillips with his girlfriend Caitlin. Henry died from a Fentanyl overdose, the drugs delivered via the Dark Web. Supplied

“He wouldn’t take heroin in a million years and then somehow he ends up taking Fentanyl.”

These days Ryan Phillips is a deputy secretary at Victoria's Department of Justice, handling Corrections and Justice Services. He recalls that Henry was at home on March 9, 2017, said "good night" to his father and didn’t wake up.

When the devastated family gathered at the house Henry’s girlfriend, Caitlin, gave Ryan a password to access his brother’s computer that showed a Dark Web account: “There were purchases similar to eBay, where customers rate products like online shoppers.

“The dealers were given stars according to quickness of delivery, quality of package disguise and the quality of the product.”

The order forms are frighteningly professional-looking. Order dates, expected express post delivery dates (free priority shipping!) and itemised billing are included.

Fentanyl can be fatal through accidental contact. And yet it is banging around the country in planes, trucks and posties’ motor scooters with no one knowing the danger. One split, one drop and the powder becomes airborne, creating an immediate hazard.

Ryan Phillips saw one of the sellers had a code name that made him suspect a Melbourne link. And that is when he contacted Victoria Police.

Once Igor Rusmir had the file he realised he needed a crash course in computers. “I was brand new to all this and so I went to E-Crimes (the police squad that works the Web) to learn what I could. They were fantastic and without them we wouldn’t have been able to go any further.”

Shortly before he died of an overdose, Henry had asked online if 40 milligrams of Fentanyl was safe. The drug is so powerful that two milligrams can be fatal.

Many were sceptical about Rusmir’s investigation. No one was seizing Fentanyl in Victoria and the Dark Web was too hard to penetrate.

Fentanyl is 50 times more powerful than heroin and 100 times more powerful than morphine and has caused an epidemic of fatal overdoses in the US and Canada. So what is the attraction? For the dealer, it is cheap and - as only tiny amounts are needed - relatively easy to import.

It is often mixed with other drugs to increase yields by up to 1000 per cent.

The computer records showed Henry Phillips bought 40 milligrams from a dealer on the Dark Web site Dream Market. Police found that after he placed the order it was sent on March 5, 2017, and arrived two days later. The quick turnaround meant the dealer must be somewhere in Australia.

Eventually, with the help of Australia Post, they found the delivery was from Victoria.

Rusmir gradually identified the Melbourne source’s online profile. His customers had given him a five-star rating for delivery and product purity – even though he was selling possibly the most deadly illicit drug ever made. (It is also incredibly dangerous for police, but more of that later.)

Now came the sting. In January 2018, E-Crime detectives bought 100 milligrams of Fentanyl powder for around $450 in Bitcoin.

So dangerous is the drug that when it was tested at the police forensic lab the wing was cleared. A second buy was made – this time of 100 millilitres of liquid. It arrived labelled “Perfume Forever”. Again it was Fentanyl.

The Dark Web dealer was the exact opposite of what you would expect. A respected national manager in an established firm, he was earning around $150,000 from his day job.

“You would never pick him," says Rusmir. "He looked like just about any other office worker in a suit.”

The man, who we'll call “Richard”, was 45 years old, a loving father of two daughters and a drug dealer. Not that he made a fortune – a long-time user, he became addicted to Oxycontin to manage pain.

In 2012 he decided Fentanyl was a cheaper option and began importations. In 2016 he began selling part of his shipment to pay for his own addiction.

He would prepare his sales on the kitchen bench near his two daughters. “He seemed unaware of any danger,” says Rusmir.

Then the target disappeared. In May 2018 the site Dream Market banned the sale of Fentanyl after multiple deaths in the US. Eventually he surfaced on another Dark Web platform – complete with his five-star rating.

When police came knocking it was a little confronting for Richard. Not only had he been pinged as a drug trafficker but due to the toxicity his house was declared a biohazard, meaning the place was searched by clandestine lab experts fully kitted in protective suits.

To the man in the suit it must have seemed like he was being raided by Martians. He had a panic attack and needed ambulance staff to calm him via a 000 call.

Clandestine lab experts wearing protective suits remove evidence from Tony Mokbel's speed lab in 1997. Pat Scala

Here is the hidden danger of Fentanyl. Investigating police face health dangers from the fumes. Many years ago police found they were getting high when seized cannabis was burned, then drug police couldn’t sleep for days from the fumes at speed labs.

But Fentanyl is on another level. In Pittsburgh, 18 SWAT team members collapsed and were hospitalised after a table containing drugs about to be bagged was knocked over in a raid. They had been overcome by airborne particles.

Such is the risk that police from the Drug Taskforce may need to be equipped with the overdose antidote naloxone, commonly known as Narcan, for protection from accidental contact.

Richard immediately co-operated with police, to the extent that when another Fentanyl shipment arrived at his home he alerted detectives.

In March he pleaded guilty to trafficking a drug of dependence and was sentenced to a community corrections order with 300 hours of community work.

In the darkest of ironies, he is supervised by Ryan Phillips’ staff at the Justice Department.

He was no big fish, he didn’t make a fortune and he will never do it again. But the drugs he sold resulted in a young man dying on the other side of the country.

For that family it is a life sentence.

At the centre of the US opiod crisis is a painkiller responsible for more deaths per year than heroin, and there are signs a similar crisis may emerge in Australia.

“Such a tiny amount can kill,” says Phillips. “Henry didn’t stand a chance.

“The packages were delivered to my parents’ post office box in [the Perth suburb of] Swanbourne. It was picked up like any other parcel.”

In the weeks and days before his death, Henry was looking forward to the future. The day before he had a job interview at a major hospital and felt he nailed it. The morning of the day he overdosed he met his mentor for coffee, telling him the interview went well. He texted a mate to confirm they were going surfing the next day.

“People are taking this without understanding that this is so toxic. This will get much worse unless people are made aware of the dangers,” says Phillips.

There clearly is a major lag in the law here. The quantity required to be convicted of trafficking a commercial quantity of Fentanyl is 50 grams - 50,000 milligrams. Yet a fatal dose can be as low as two milligrams.

When Igor Rusmir started his investigation, he found six dealers selling Fentanyl on 10 different platforms. Now there are 106.

Rusmir, 39, arrived in Australia nearly 20 years ago as a refugee and joined the police 10 years ago. He was 11 when the Balkan wars started and he moved to Australia with his parents and sister when he was 19.

Earlier this year, he won the Mick Miller Detective of the Year Award for “outstanding exemplary service, professionalism and investigative capability”.

Senior Detective Igor Rusmir receives the Mick Miller Detective of the Year Award from Assistant Commissioner Tess Walsh (left), Deputy Commissioner Wendy Steendam and Mick Miller's son Geoff. Victoria Police

When I ask him why he became a policeman, the slightly built Rusmir says quietly: “Because I did not have the physique to be a bikie.” Clearly Serbian humour is on the dry side.

He then says he joined “because I wanted to do something different and I wanted a career where you gave something back”.

He also wanted to help the country that had helped his family. He says many Serbians, scarred by the civil war, were scared of police. When he joined he was the only officer of Serbian descent. “Now there are a dozen.”