The appearance of the suspects (i.e. type of hair, heavy or slim, left or right-handed and male or female) matters a lot! These are the things you have to match the PE with. But you need the appropriate skills to find out:
- if a footprint is from a heavy or slim person
- if a note is from a right- or left-handed person
- if a thread is from male or female's clothes
- if a hair is from a person with curly or straight hair
But the appearance of the crime scene doesn't matter at all. Only what you find there matters.