Scientific tests are used to determine the evidence against the suspect

What is the blood group of the criminal? You have been provided with 4 blood serum samples (labelled 1-4) plus a blood sample taken from the crime scene, labelled CS. Samples 1-4 are from known blood groups - A, AB, B and O. When a blood sample and a serum sample from different blood groups are mixed together they will clump (clot). Use a dropper to add 1cm³of the serum samples 1-4 to separate test tubes. Add 1cm³ of the crime scene blood to each serum sample in the test tubes. Carefully shake the tubes and observe each of them to see if the blood has clumped. If there isn't any clumping, then the serum blood group matches the crime scene blood group.