Hair evidence is considered "class" evidence because the hair can be connected to a certain group.
Explanation:
The hair evidence alone can't be used to pinpoint John Doe in the robbery because he also came to deposit his weekly paycheck so may be the hair drop at that time in the bank. The other reason is that may be the hair has been dropped by the real thieves in order to be caught the John Doe in the crime. Hair evidence is considered "class" evidence because the hair can be connected to a certain group.
