The evidence must be impartial.

This is the law." Gregory said without looking up: "But why ?" Mr.Paramor took his violets out of the water, and put them to his nose.
"How do you mean--why ?" "I mean, why this underhand, roundabout way ?" Mr.Paramor's face changed with startling speed from its haunting look back to his smile.
"Well," he said, "for the preservation of morality.

What do you suppose ?" "Do you call it moral so to imprison people that you drive them to sin in order to free themselves ?" Mr.Paramor obliterated the face on his blotting-pad.
"Where's your sense of humour ?" he said.
"I see no joke, Paramor." Mr.Paramor leaned forward.
"My dear friend," he said earnestly, "I don't say for a minute that our system doesn't cause a great deal of quite unnecessary suffering; I don't say that it doesn't need reform.

Most lawyers and almost any thinking man will tell you that it does.

But that's a wide question which doesn't help us here.