Microscopic comparisons of firearms evidence have changed little since the development of the ballistic comparison microscope over 70 years ago. The Sacco and Vanzetti case, tried in 1921, where the defendants, known and very vocal anarchists, were accused of murder during a robbery, is perhaps the most famous of the early uses of ballistics in American Law. It was then, and is now, considered a definitive proof of a suspect’s involvement in a crime if a particular weapon used can be traced to the defendant:

…I say to you on this vital matter of the No. III bullet…Take the three Winchester bullets that were fired by Captain Van Amburgh at Lowell and take the seven United States Bullets that were fired

by Mr. Burns at Lowell, and, lastly, take the barrel itself which we will unhitch for you, and determine the fact for yourself, for yourselves…Take the glass, gentlemen, and examine them for yourselves. If you choose, take the word of nobody in that regard. Take the exhibits yourselves. Can there be a fairer test that I ask you to submit yourselves to?1