But, like plots, that is a whole other workshop. That, too, depends. So, let me give you some examples. For example, you might have a brown hair discovered at the scene of the crime, and two or three suspects who have brown hair. Or maybe a partial fingerprint from the jilted lover on a can of Diet Coke found in a room of a house she claims she was never in.
Dialogue can be a clue.
That woman who says she was never in that house provides a clue. The man who says he never, ever wore such ugly shoes or never, ever hit his wife provides a clue. Whether it's an accurate clue or not is another matter. Relationships can be a clue. You might think all these are relatively easy, and you'd be right.