Journalist Peter Hitchens wrote the following in the connection with the events in Salisbury, England, involving a former Russian double agent and his daughter, but it is worth keeping in mind always:
The presumption of innocence is not just a great liberty and defence against state power. It can also help investigators avoid the obvious conclusion, and carry on pursuing other lines of inquiry which might otherwise escape attention.
After all, isn’t the point of almost every detective story we read and see on the TV that the police tend to arrest the obvious suspect, and it is hardly ever the right one? As Sherlock Holmes used to say, as he began work with his magnifying glass, and his clients pressed him for an instant verdict ‘It is a capital error to theorise without data’. Also, it is amazing how wrong the obvious solution can be. I take the opportunity, yet again, to urge everyone to read Josephine Tey’s severely brilliant novel ‘the Franchise Affair’, in which dogged, sceptical inquiry reveals that something apparently impossible is true, and that the obvious, unpopular suspects in a crime are (in that particular case) wholly innocent of it. Once you have read it you will never view a criminal case or trial in the same way.