And he knows, as delegates to WAN-Ifra's Digital Media Asia event in Kuala Lumpur learned.
The London journalist whose name card reads 'special projects editor' was new to Twitter when he found he was at the heart of a stream trying to found out what happened when a man died during protests during the G20 talks.
What journalists had reported as police being pelted with bricks while they tried to save a man's life turned out to have a much less attractive reality: When Lewis used Twitter to seek eyewitness reports and video, he gained access to footage showing a policeman knocking the man down.
The revelation - in line with the Guardian's 'story behind the story' slogan- changed the course of reportage.
But he says citizen Tweets cannot always be trusted. Take the example of the London riots, where a rumour about animals being let out of the city zoo by rioters was compounded by someone who Tweeted a picture of a tiger on the loose... which was identified as a much older image of a tiger in Italy.
Despite the risk, Twitter has a habit of policing itself. Lewis says citizens will also puncture rumours quicker than would otherwise be the case.
Does Lewis Tweet on his own behalf or that of his employer? Does he report to the editor first? These and other questions came from delegates.
The answer to the first question is 'both' with the same standards applied as for normal journalism.
And he Tweets first; "if we report to the editor first, we'll be second," he says.