In a guest post for the Online Journalism Blog, Paul Lewis shows how Twitter helped the Guardian in its investigations into the deaths of news vendor Ian Tomlinson at the London G20 protests and Jimmy Mubenga, the Angolan detainee, while he was being deported from Heathrow.

This originally appeared in the book Investigative Journalism: Dead or Alive?, which also includes another chapter previously published on the blog: Has investigative journalism found its feet online?.

Investigative journalists traditionally work in the shadows, quietly squirrelling away information until they have gathered enough to stand-up their story. That silence reassures sources, guarantees targets do not discover they are being scrutinised and, perhaps most importantly, prevents competitors from pinching the scoop.

But an alternative modus operandi is insurgent. It is counter-intuitive to traditionalist mind-set, but far more consistent with the prevailing way readers are beginning to engage with news.

Investigating in the open means telling the people what you are looking for and asking them to help search. It means telling them what you have found, too, as you find it. It works because the ease with which information can be shared via the internet, where social-media is enabling collaborative enterprise between paid journalists and citizens who are experts in their realm.

Journalism has historically been about the hunt for sources, but this open method reverses that process, creating exchanges of information through which sources can seek out journalists. There are drawbacks, of course. This approach can mean forfeiting the short-term scoop. At times, the journalist must lose control of what is being investigated, how and by whom, and watch from a distance as others make advances on their story.

They have to drop the fallacy that their job title bestows upon them a superior insight to others. But all these are all worthwhile sacrifices in the context of what can be gained.

This is illustrated by Guardian investigations into the deaths of Ian Tomlinson, the newspaper seller who died at the London G20 protests in 2009, and Jimmy Mubenga, the Angolan detainee who died while being deported from Heathrow on 12 October 2010. In both cases, eliciting cooperation through the internet – particularly Twitter – allowed us to successfully challenge the official accounts of the deaths.

In the second part Lewis explains how he used Twitter and Flickr to pursue his investigation into the death of Ian Tomlinson.

UPDATE: The stories described in these posts can also be seen in this video of Paul speaking at the TEDx conference in Thessaloniki: