Evidence with individual characteristics can definitely be identified with a person or source if sufficient microscopic or accidental markings are present. Some examples include fingerprints, handwriting, firearms, bullets, tool marks, shoe prints, and pieces of glass in cases in which broken edges can be matched. Evidence with class characteristics, no matter how thoroughly examined, will only be placed in a class or group. A definite identification can never be made. There is always a possibility of more than one source for the material found.
Some examples are hair, fibers, blood, soil, paint, and glass fragments.
It is, of course, desirable to have evidence that can be positively identified, but cases can be made on evidence with class characteristics only. This type of evidence can help build the case of circumstantial evidence or prove an alibi false. Just as important, this type of evidence can give a definite negative, i.e., proving positively that a particular piece of evidence did not come from a particular source. A bloodstain can be proved not to be from an individual. A better case can be made with class evidence when the evidence has either a greater number of identifying features or a greater number of different types of evidence.