There's been a major crime near where I live.
As a local resident who frequently passes the scene, I've been interviewed.
I gave the police some information on a couple of unusual things I've seen recently and, as a result, gave a written statement.
Afterwards, they asked permission to take my fingerprints and DNA sample, so I agreed.
I can remember when the taking of fingerprints and DNA from witnesses, not just suspects, was introduced, there was a lot of opposition.
So what's the problem ?
I do get that instinctive objection to an intrusion of my privacy feeling, but in reality, does it matter ?
