What are some of the challenges in analyzing tool marks? (forensic science)

If there is no finger prints or dna and ask me if its about forensics

Most major challenge in analyzing tool marks is due to their micro size. As we are talking about forensic science, most of the things there are of very small size. So, dealing with objects at that range is quite challenging 

When we mark something, for our reference, then the wideness of that mark might create an error, due to greater size just as compared to the system of the experiment

Hope this helps!