On social media, especially in crisis situations, rumors easily spread.
Therefore, LEAs use social media to refute rumors, as they have a strong voice in social media that other refer to as a trusted source.
During the UK Riots in 2011 a large part of the communication has been to refute rumours.
In: Sebastian Denef, Petra Saskia Bayerl, and Nico Kaptein (2013): Social Media and the Police—Tweeting Practices of British Police Forces during the August 2011 Riots. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (Paris, France, April 27–May 2, 2013). CHI’13. New York, NY: ACM Press.
The West Midlands Police Force use social media, primarily Twitter, to counter rumours. They for instance tweeted officers standing outside the station to fight a rumour of an attack on their police station.
In: Bartlett J., Miller C. (2013), @metpoliceuk How Twitter is changing modern policing the case of the Woolwich Aftermath. London: Demos.