Who cut off Vincent van Gogh's ear and why?

It actually was not Van Gogh's entire ear, but his earlobe. He had been suffering from mental illness, and had been having hallucinations and delusions. He was in a brothel when he did it. He wrapped it in tissue, gave it to a prostitute, and asked her to take care of it. It has never been confirmed, but there are some that theorize that the mental illness was brought on to exposure to leads in his paints.