Someone came to your house looking for something you don't sell?
Considering everything that has transpired, my feelings are this person is casing your home. Perhaps, to see if anyone is home in the day. Could just be a coincidence, then again, maybe not. Make sure you tell the police this.
Also, make sure your home/renters insurance is paid up to date. Don't leave anything out and make sure your locks are all good ones. One last thing, if I don't know someone and they knock on my door, I don't even answer it. Heck, if someone I do know knocks on my door with an unexpected visit, I rarely answer my door. Unless I'm available and want company.
I hope this all works out for you. Keep us updated.