They were dead, at the hands of a person unknown.

This was strange, to be met by an unknown person in a city where he had never been before.

And the unknown person who had set up this Web site didn't accept any other key.

Immediately afterwards, though, his father is shot by an unknown person.

"And how did you think this unknown person might have gotten hurt?"

The only thing he can recall is what some unknown person has suggested to him.

The art gallery owners would take no risk on an unknown person.

We think it's natural to court a totally unknown person in a bar or club.

An offer to change money by an unknown person on the street is most likely a scam.