Secret hair in In And Out
When on the first investigation (In And Out), go to the cloth on the bed next to the dead woman and use the magnifier. Then, use the tweezers to pick up the hidden hair.

Pawn Shop in Prints And Pauper
Evidence is hidden at the pawn shop, to the right of the garbage can on the ground, There is a ring that you do nothing to. Open the object with the microscope above the ring. Tweeze the hair and swab the stain. Then, go back and access the object. Take it, then talk to Lane Jackson (the man at the pawn shop).

Sweater thread in Garvey case
Go to the iron rod. Use the magnifier. Move all the way down the rod with the magnifier and you should find a thread from a sweater.

Help from partner
You can ask your partner for a hint about the case. You can see in what area you have not done, such as locations that you have not thoroughly searched.