By Dannie Plachta (?-?).
First appearance: Worlds of IF, July 1966.
Reprinted quite a few times (HERE).
Short short short story (2 pages).
Online at Archive.org (HERE).
"He came out of nowhere — and could never go back!"The stranger isn't a criminal per se, but human nature being what it is, his victims could justifiably regard what he does as a criminal act.
- We looked but we couldn't find any biographical information about our author, Dannie Plachta; however, the ISFDb does have a short bibliography (HERE).
The bottom line:
"Well, that's it," I said after we had waited for another five minutes and found ourselves still in a state of pleasantly welcome existence. "The ChronoGuard has shut itself down and time travel is as it should be: technically, logically, and theoretically...impossible."
"Good thing, too," replied Landon. "It always made my head ache. In fact, I was thinking of doing a self help book for science-fiction novelists eager to write about time travel. It would consist of a single word: Don't.”
— Jasper Fforde