Back in its 2013 heyday, when bitcoin soared from below $100 to over $1000 in the span of a few months (in no small part thanks to the collapse of the Cyprus banking system) there was only one real Bitcoin exchange: Magic: The Gathering Online Exchange, or Mt. Gox as it was better known, which had become the world's largest hub for trading the digital currency. And then, as mysteriously as it had appeared, Mt. Gox went dark, and filed for bankruptcy after nearly half a billion dollars worth of bitcoin "disappeared."

We wrote at the time:

For a case study of a blistering rise and an absolutely epic fall of an exchange that i) was named after Magic: the Gathering and ii) transacted in a digital currency which many have speculated was conceived by the NSA nearly two decades ago and was used as a honeypot to trap the gullible, look no further than Mt.Gox which after halting withdrawals for the second (and final time) has finally done the honorable thing, and filed for bankruptcy. As the WSJ reports, "Bitcoin exchange Mt. Gox said Friday it was filing for bankruptcy protection after losing almost 750,000 of its customers' bitcoins, marking the collapse of a marketplace that once dominated trading in the virtual currency. The company said it also lost around 100,000 of its own bitcoins. Together, the lost bitcoins would be worth approximately $473 million at market prices charted by the CoinDesk bitcoin index, although the price of Mt. Gox bitcoin had fallen well below that index after it stopped bitcoin withdrawals in early February."

The punchline: speaking to reporters at Tokyo District Court Friday after the bankruptcy filing, Mt. Gox owner Mark Karpelès said technical issues had opened the way for fraudulent withdrawals, and he apologized to customers.

"There was some weakness in the system, and the bitcoins have disappeared. I apologize for causing trouble."

In other words, oops sorry, several hundred million in Bitcoin is unaccounted for but blame the "system weakness." This promptly led to various artistic interpretations on the Mt. Gox logo, such as this one:

Some were confused if Karpeles was going to get away with nothing more than an excuse, even if - as many speculated - he had personally fabricated exchange data entries and embezzled millions of dollars for his own account.

As a reminder, when it filed for bankruptcy in February 2014, Mt. Gox said 750,000 customer bitcoins and another 100,000 belonging to the exchange were stolen due to a software security flaw. The lost funds represented the equivalent of $480 million at the time of the bankruptcy filing. Mt. Gox also said more than $27 million was missing from its Japanese bank accounts. Karpeles, who had blamed hackers for the loss, later said he had recovered 200,000 of the lost bitcoins.

Earlier today we got the answer when nearly 18 months after his infamous apology, Mark Karpeles was arrested in Tokyo. FT reports that Japanese police have arrested Mark Karpelès, the head of the bankrupt Japan-based bitcoin exchange Mt Gox. The arrest charge is that he made an illegal entry to the system in February 2013 and increased the balance of his account by $1 million.

And yet, a year and a half after the exchange insolvency, nobody truly knows what happened:

The alleged crimes involved are hard to pin down, say police sources, because of the absence of a specific laws governing the virtual currency. Police have acknowledged privately that there technical elements of the alleged disappearance of nearly $500m that "are still not properly understood".