A homicide investigator typically uses ballistics and serial numbers of weapons checked via a vast network of gun shop records, manufacturer IDs and crime databases. But those sleuthing tactics are fast becoming old-school science as a new era of weapons increasingly hits the nation's streets: untraceable 3D printed guns and silencers like the ones found this week on suspected killer Luigi Mangione.

Ghost guns, like the weapon the NYPD said UnitedHealthcare shooting suspect Luigi Mangione had when arrested, can be assembled at home.