Clearly the problem here is that the security services need much bigger haystacks...
I don't think it is about "security". After all, no one has said that anti-encryption laws would have made the slightest difference here - for one thing the investigation has only just started, so no one knows.
I think it is about being able to monitor and control dissent in society. Bombs and terrorists are just a convenient excuse for getting what they want. This is a ratchet, once they get this, they will just demand the next bit of intrusive monitoring on their list.