Research statement ideas got used by interviewing committee

There is of course the possibility that the person you've accused actually had the same idea independently. It's certainly suspicious, the moreso if when you were interviewed that person did not say "I like your idea and have actually been working on something similar". I agree with the suggestion that you contact the chair and raise the issue, but be polite and nonconfrontational about it. If you say "I think this guy stole my idea" it could be less effective than "I came across something similar to what I had proposed ... since Prof X didn't indicate he was working on this, I found it interesting that he published something so similar to what I proposed."

The thing to keep in mind is that it is a very gray area... this person might have come across your idea, forgotten about it, and later decided to pursue this idea without actually being consciously aware the idea came from your proposal. And, you say much of the work goes beyond what you actually proposed. So I think the chair should be informed, but I wouldn't expect much to come of it unless he's known as a repeat offender.

Contact the department chair, with a well-documented chain of events, and ask him to verify using the admission materials you ahd submitted to the department prior to the interview. Even if the plagiarist got away this time, he would know that he/she could not pull it off again, as people around him/her had gotten to know of this - and no one would want to work with someone who can potentially steal your ideas, right?