The shooting, which left four dead and 17 injured, is just the latest spurt of mass violence made possible by the small 3D-printed part known as a “conversion device,” “Glock switch” or “auto sear.”

A $100,000 reward is still on the table for anyone who offers information that leads to the suspects of a shooting in Birmingham, Alabama, where four were killed and more than a dozen were injured. The suspects apparently targeted at least one person in the area.

An Alabama police officer is under investigation for allegedly shooting and killing a 68-year-old man, according to authorities. The incident occurred around 5 p.m. on Sunday in Muscle Shoals when officers responded to a call in a residential neighborhood,