The anonymous source behind the huge leak of documents known as the Panama Papers has offered to aid law enforcement officials in prosecutions related to offshore money laundering and tax evasion, but only if he is assured that he will not be punished. “Legitimate whistle-blowers who expose unquestionable wrongdoing, whether insiders or outsiders, deserve immunity from government retribution,” the source, who has still not revealed a name or nationality, said in a statement issued Thursday night. The source, who uses the pseudonym John Doe but whose gender is not known, said that the papers could spur thousands of prosecutions, “if only law enforcement could access and evaluate the actual documents.”