We found one in our yard once that was over 5 foot 3 inches long (couldn't get him completely straight)! We're not 100% sure what he was but after looking at pictures decided he might be an eastern king snake. Took him waaaay back from the house to a creek. The sucker was back and up in my holly bush the very next day! We know it was the same snake because he had eaten something and had a bulge in his belly. We re-rehomed him again to another creek over a mile away...this time he stayed gone! We wanted to let him stay around but DH is deathly afraid of snakes...if he had come across this snake by suprise he would have had a heart attack! The one we found was a lot bigger around than the one you killed, too. Yours looks like what my grandmother used to call a coach whip (long and slender). Lots of snakes will shake their tails to warn you off.