Totally just call the local police department (non emergency number) and say you don't mean to be a bother, but this weird thing happened, and you know you are probably imagining the worst, but thought you'd mention it to them just in case there has been someone missing or something.

Probably it's some weird coincidence - dogs dragged some clothes there from someone's trash or clothesline, or some drunk kids were fooling around and left behind some things. A murderer probably wouldn't leave the clothes lying right by the path where someone could see them.

Creeepy, though!