I have never heard of the Smiley murder cases so I looked it up. 40 young men in 11 states? The article stated 12 of those accidental deaths/possible murders had a “smiley face” used as graffiti nearby. Almost all were white young men, athletic and had been recently to a bar/drinking. Not sure if there is a serial killer or not... but it certainly is an interesting case.
The majority were in Wisconsin, mostly along the Mississippi River.