For me, Mark is indeed the chief suspect, but I know no evidence that will rule out other possibilities -- including embezzlement by some other MtGOX manager or staff, theft of paper wallets by a physical intruder, hacking by a complete outsider, etc..

The people who were suing MtGOX in the US claimed to have evidence of wrongdoing, but unfortunately the withdrew their lawsuit to support the Sunlot proposal.

We can only hope hope that a police investigation will someday find the culprit.

Mizuho held non-Bitcoin currency on behalf of Tokyo-based Mt. Gox and its customers, according to the amended U.S. complaint by Gregory Greene, an Illinois resident who [allegedly] lost $25,000 when [the exchange] shut down,” said Reuters. “The U.S. suit accuses Mizuho of knowing of Mt. Gox’s fraud, of not segregating funds that belong to Mt. Gox from those of its customers and of continuing to provide banking services that inflated losses for Bitcoin customers.