गूफ़

Whe Linda takes Marty's gun in for ballistics testing - to see if it was the one that killed her brother - the expert says it doesn't match. ("They're not even close.") But looking through the comparison microscope, it's apparent that if the right image is moved up slightly, all the markings from the lands and grooves would match perfectly. The expert then switches the bullet to the one that killed Clark, and the same images as before are used; only this time, the expert moves the images and everything does align.