Setting your scene for a mystery requires evocative imagery to convey mood and is best created by seeing the world from the perspectives of your point of view character.
Who is the point of view character in the picture above? The woman who is probably the mother of the child? But what if she's not the mother? What if she's a social worker? What if she's the detective? What if she's the murderer who is also the boy's mother? What if she killed her husband?
What if the point of view character is not in the picture but watching from afar? What if this unseen person is the investigator or detective in your mystery? What if she doesn't trust the woman holding the little boy's hand?
What if the observer is the murderer who gets sick pleasure from watching the mother and child grieving?
The setting of a scene changes when you view it through the eyes and feelings of different characters. So forget for a moment how you would set this scene; instead ask how your point of character experiences it.