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Not really the cloak and dagger example you're looking for, but may serve others to shake out some low hanging fruit.
Quite a few years back, got a tip-off that a senior official was paying themselves through a backdoor.
Sent off questions to said official, asking them about the allegations, and followed up with a phone call, to which the official responded: "I don't want to talk to you."
Hmmm. I tried ringing around staff members in the Office of the Prime Minister, especially the ones who I knew loathed their Chief of Staff. But they were all too terrified of losing their jobs, even when I suggested 'cunning plans' for emails, faxes, paper drops etc. So, no evidence, no story.
Hmmm. In the end, my breakthrough was quite simple. Had an 'aha' moment, rewrote the questions addressing him personally to general questions about "anyone" in his office making backdoor payments to themselves.
He again refused to comment, so I quite happily wrote a "refusing to comment" story on the allegations, which caught the eye of the chief auditor, who ordered in the forensic investigators, and the Chief of Staff got de-staffed, eventually getting a two year prison sentence.
In my haste to be an investigative whizz kid, I had forgotten good ol' KISS. Got the job done, without endangering any sources.
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