It looked like a dream transaction. Greece's debt-burdened government would borrow at sharply lower rates while JP Morgan, the US investment bank that underwrote the €280m structured bond, would gain access to a small but fast-growing market for sophisticated debt instruments.

Six months later, the deal is under scrutiny by two Greek investigators, amid allegations of incompetence and corruption at four state-controlled pension funds, which bought the bond from an Athens brokerage at inflated prices. Up to 40 Greek officials and brokerage employees could face criminal charges.