@BanjoPartisan @JSDorn @d0c40r0 >They can track type writers too. Each mechanical letter is slightly different.
Yes, they can tell if it is likely multiple letters came from the same typewriter, but typewriters don't write the typewriter serial (if any) to the paper unlike printers with tracking dots.

It's often the case that a printer serial is tied to the purchases identity via a proprietary purchase process, which doesn't happen with typewriters.

Generally paper analysis would be relied on more if printer tracking dots are not found.

>It's similar to how they can tell what gun a bullet was fired from.
You cannot, as each round of high velocity lead abrades the barrel differently and tends to be severely deformed on hitting an object.

You can determine that say such bullet is a .308 one and therefore any suspects who only have .223 and .22 rifles didn't fire such bullet.

Dodgy ballistics has resulted in the imprisonment of many innocent people.

Although, if a firearm like a shotgun was used to murder someone at point-blank range, blood ends up in the barrel(s) and can be detected quite a while after unless the blood has been cleaned out.