The Weeks Update:
In the wake of the killings in Brussels a number of people were arrested, although on Monday a man charged with direct involvement, was released due to a lack of evidence. The challenge now is to track down other militants and break up existing IS cells before they strike again. That won't be easy since the exact number isn't known and - as Brussels illustrated - there will always be terrorist suspects who evade the intelligence gathering net, especially if sections of that net are already weak. Joining Investment Perspectives host Juliette Foster with more analysis is Sir David Omand, the former Director General of the government intelligence organisation GCHQ, and Professor John Weeks, Share Radio's regular economics commentator.