So unfolded the abhorrent events on the Boston Police Twitter feed today. The feed – with its updates, instructions and attempts to crowd source — went out to the Police Department's 110,000 followers. Through Twitter's network effect, many, many more were able to see the Boston PD's messages (the tweet calling for video was re-tweeted over 3000 times).

Social media was used by a range of other services too, such as the Emergency and Medical Services, the City of Boston, and the Massachusetts Emergency Management Agency, reflecting the way social media has increasingly become integrated into government communication.

As has become typical for tragedies nowadays, non-government groups also quickly stepped in to help online, Google's Person Finder being but one example.

As Bill Braniff, Executive Director of the National Consortium for the Study of Terrorism and Response to Terrorism, put it: 'Authorities have recognized that one [of] the first places people go in events like this is to social media, to see what the crowd is saying about what to do next. And today authorities went to Twitter and directed them to traditional media environments where authorities can present a clear calm picture of what to do next.'

The communication value of social media can, however, rub up against security considerations. An early AP report claimed mobile coverage had been shut down to prevent detonation of other explosive devices (this later proved to be inaccurate). But this is increasingly a consideration for police forces in dealing with incidents like these. And it is a response that has already been used in protest situations: in August 2011, San Francisco's Bay Area Rapid Transport authority shut down cell phone coverage to prevent a protest; Prime Minister Cameron also considered it in response to the London riots.

Hopefully, the same tools will prove helpful in apprehending the perpetrators of this horrific crime.