Image copyright Facebook/Quadriga Image caption Gerald Cotten

When the 30-year-old founder of a Canadian cryptocurrency exchange died suddenly, he took the whereabouts of some C$180m ($135m; £105m) in cryptocurrency to his grave. Now, tens of thousands of Quadriga CX users are wondering if they will ever see their funds again.

In 2014, one of the world's biggest online cryptocurrency exchanges - MtGox - unexpectedly shut down after losing 850,000 Bitcoins valued at the time at nearly $0.4bn (£0.3bn).

Its meltdown shook investors in the volatile emerging marketplace - but the calamity at the Tokyo-based company proved a boon for a new Canadian online cryptocurrency exchange.

"People like the fact we're located in Canada and know where their money is going," Quadriga CX founder Gerald Cotten said at the time.

Some five years later, Cotten's sudden, untimely death has left thousands of his customers scrambling for information about their own missing funds.

"We don't know whether or not we're going to get our money back," Tong Zou, who says he is owed C$560,000 - his life savings - told the BBC.

"There's just a lot of uncertainty."

This month, Quadriga - which had grown to become Canada's largest cryptocurrency exchange - was granted temporary bankruptcy protection in a Canadian court.

The firm said it had spent the weeks since Cotten's death trying desperately to "locate and secure our very significant cryptocurrency reserves".

Image copyright Reuters Image caption Broken representations of the Bitcoin virtual currency

In court documents, Quadriga says it owes up to 115,000 users an estimated C$250m - about C$70m in hard currency and between C$180m an C$190m in cryptocurrency, based on recent market rates.

It believes - though it's not certain - that the bulk of those millions in reserves was locked away by Cotten in cold storage, which is an offline safeguard against hacking and theft.

For now, all trading has been suspended on the platform.

Bernie Doyle, CEO of Refine Labs and head of the Toronto chapter of the Government Blockchain Association, calls what's happening at Quadriga a "seismic event" in the industry.

The world of digital currency has little regulatory oversight and a history of volatile prices, hacking threats, and minimal consumer protection.

Mr Doyle says this only adds to the nascent sector's already "checkered history".

But he says "it's really unfortunate that the ecosystem takes a hit" amid one firm's problems.

Image copyright Reuters Image caption The theft involved the lesser-known IOTA cryptocurrency

What happened at Quadriga?

Court documents filed in late January offer some insight into the company.

Quadriga had no offices, no employees and no bank accounts. It was essentially a one-man band run entirely by Cotten wherever he - and his laptop - happened to be, which was usually his home in Fall River, Nova Scotia.

It used some third-party contractors to handle some of the additional work, including payment processing.

His widow, Jennifer Robertson, says she was not involved in the company until her husband died suddenly on 9 December in India from complications related to Crohn's disease.

In an affidavit, she says she has searched the couple's home and other properties for business records related to Quadriga, to no avail. The laptop on which he conducted all the business is encrypted and she doesn't have the password or recovery key.

An investigator hired to assist in recovering any records had little success.

It was also recently revealed the company somehow inadvertently transferred Bitcoins valued at almost half-a-million dollars into cold storage in early February and now can't access them.

But Quadriga's troubles didn't start with missing coins. The company's liquidity problems began months earlier.

In January 2018, Canadian bank CIBC froze five accounts containing about C$26m linked to Quadriga's payment processor in a dispute over the real owners of the funds, an issue that ended up in court.

Image copyright Supreme Court of Nova Scotia Image caption A photo of bank drafts submitted in Quadriga court documents

The company says it also has millions in bank drafts it has been unable to deposit because banks have been unwilling to accept them.

Ms Robertson's affidavit to the court included photos showing stacks of bank drafts placed on a kitchen stove.

Those banking disputes contributed to a "severe liquidity crunch" at the company, with frustrated users facing delays and difficulties trying to access funds.

Who was Gerald Cotten?

In photos and interviews, Cotten comes across as a clean-cut business school graduate who tended to favour the casual shirts and jeans uniform of a tech entrepreneur.

In a statement, Quadriga called him a "visionary leader" who was in India for the opening an orphanage for children in need when he died.

His friend Alex Salkeld described Cotten as a helpful, easy-going young man keen to contribute to the community of cryptocurrency enthusiasts.

"I don't think you'll find anyone willing to say anything bad about him," he told the BBC.

Mr Salkeld said once a week Vancouver Bitcoin Co-Op members would all head over to the Quadriga's then-offices "and just talk Bitcoin".

Like others at the time, he said Cotten saw Bitcoin as a technology with the potential to change the world - a virtual currency free of governments and the banking system.

Mr Salkeld said that since Cotten died, those who knew him have been going back-and-forth over how he could possibly have failed to have a contingency plan in place.

Image copyright Courtesy Alex Salkeld Image caption Gerald Cotten in 2014 showing Alex Salkeld's daughters how to use a Bitcoin automatic teller

But amid rampant talk online about possible fraud related to the missing coins, Mr Salkeld said that, to him, "it's looking like a tragic series of unfortunate events strung together in a really unlucky way".

Cotten's last will and testament also gives some hints as to his life and assets.

The document, signed shortly before his ill-fated trip to India, shows he appointed Ms Robertson as executor of the estate and left her the bulk of his property.

It offers some detail into those assets: a Lexus, an airplane - he was an amateur pilot - a sailboat, and real estate in the Canadian provinces of Nova Scotia and British Columbia.

He even planned for the care of his two chihuahuas, Nitro and Gully.

The case against Quadriga

There are many who are suspicious of Quadriga's story and who doubt claims that Cotten had the only key to reserves valued in the tens of millions of dollars.

Online sleuths and industry experts have analysed the public transaction history of Quadriga wallets - which are used to store, send, and receive cryptocurrency - and have raised the possibility that the cold storage reserves might not exist at all.

That has led to concern there is more at play than poor business practices and internal company chaos in the wake of Cotten's death.

Others have wondered whether Cotten faked his own death and that this is all part of an "exit scam" to abscond with the funds.

Amid those rumours, Ms Robertson's affidavit included a copy of statement of death from a funeral home in Halifax, Nova Scotia.

The hospital in Jaipur where Cotten was treated also released a statement detailing the medical interventions he received prior to his death.

His widow says she has received death threats and "slanderous comments" online since Quadriga publicly announced its troubles.

An independent third party monitor has also been appointed to oversee the court proceedings, and is currently in possession of Cotten's laptop and other devices.

What happens next?

In an online message to its users, Quadriga said it filed for creditor protection to give it time to ensure the future viability of the company.

It also admitted it is in "the early stages of a long process and [does] not have all the answers right now".

According to court filings, Quadriga is also investigating whether some of the cryptocurrency could be secured on other exchanges and it said it's considering selling the platform to cover its debts.

A number of affected users, including Tong Zou, have retained lawyers and are seeking representation in the proceedings.

Meanwhile, Canada's main securities regulator, the Ontario Securities Commission, has confirmed it looking into Quadriga "given the potential harm to Ontario investors".