Four years ago, I received a phone call from a mysterious man keen to talk about Deutsche Bank’s accounts. Initially I was tempted to hang up. Journalists often get crank calls and this tale was particularly baffling. But in my two decades as a journalist I have learnt (the hard way) that it is difficult to tell a crank from a genuine whistleblower on the first encounter.

My colleagues duly investigated, published a story, and this week there was a denouement of sorts: Deutsche Bank agreed to pay a $55m penalty over its apparent failure to reveal a “material risk for potential losses estimated to be in the billions of dollars” in its accounts during the financial crisis.

As punishments go, this looks disappointingly feeble given the implications of this alleged accounting misstatement. The SEC says that Deutsche overstated its derivatives holdings by at least $1.5bn. However, whistleblowers insist that the amount was several times bigger, and that if the accounts had been correct in 2008 the losses might have forced Deutsche to ask for a government bailout.