Recently there were a series of arrests in Birmingham (UK), which led to six men being charged regarding a planned bombing campaign; for some background and details see: http://www.bbc.co.uk/news/uk-15054790

What is noteworthy - for this thread - is that the senior police officer responsible has publicly commented:
The actual case does not rely upon what local people were telling us, that came later - afterwards and we are grateful for that.
Some, if not all of those arrested were known in their local communities as being Jihadist "hot-heads" and who had of late become more vocal; so people began to disassociate themselves from the group and stated words similar to "The police will be calling on them soon, if they keep on talking like this".