Chewing Gum
Answer
If Martin Moor were the murderer, he would have had a severe allergic reaction to the E171 dye in the chewing gum. Therefore, he has an alibi and he is not the person who covered the lens of the security camera.
If Martin Moor were the murderer, he would have had a severe allergic reaction to the E171 dye in the chewing gum. Therefore, he has an alibi and he is not the person who covered the lens of the security camera.