Somebody somewhere knows when there's something rotten which should be brought to the public's attention.
A tip off can be an anonymous call, an email or a message from a victim perhaps, or a campaigner or lawyer.
In one case it was film actor Richard E Grant who tipped us off about conmen who were trying to flog a bogus AIDS cure in Africa.
Broadcast 1 December 2006.
The actor grew up in Swaziland, which has the highest incidence of AIDS. As he tells Paul Mason, he knew straight away this was a con.
FBI tip-off
In another case we were tipped off by FBI Special Agents. Yes they do have business cards with Special Agent on them.
Broadcast 6 November 2001
Greg Palast investigates whether the FBI were prevented from investigating the Bin Laden family.
A tip off does not have to be 100% correct
Sometimes the tip off may not be accurate but may still lead in the right direction.
A Newsnight viewer suspected companies at Heathrow were illegally employing foreign criminals. This led us to discover that the government was failing to carry out any checks to prevent foreign criminals from working airside.
The Whistleblower
The ideal tip off comes from a whistleblower who can provide full documentary evidence and eye-witness accounts from the inside, like the man who showed us how the makers of Gaviscon had cheated the NHS out of �40 million.
Broadcast 7 March 2008
When a whistleblower decides to talk they put themselves on the line, hence the rather ridiculous hat as he talks to Martin Shankleman.
Preliminary Investigation
How do we extract the nuggets of truth from a garbled account, a suspicion or a hunch?
In the early stages we "shotgun" all available sources of basic information - newspaper cuttings, legal databases and Google.
We talk to the experts in that field. We put any names we find through electoral rolls, directory enquiries etc.
Some stories stand up. Others fail to make the cut at this early stage.
How do you 'stand up' the stories which you think are promising? Click on the Leads tab.
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