“We want to know: Why? What happened?”So many questions, so much we still don’t know about the case of the woman shot to death by the Secret Service and the U.S. Capitol Police on Oct. 3, 2013, after a car chase from the White House to Capitol Hill. Her 13-month-old daughter survived in a car seat.“Did we miss something?”Barbara Nicholson is asking. The office manager of a dental practice in Ardsley, N.Y., is standing in the hygiene room, remembering the woman who used to clean teeth at this chair. Miriam Iris Carey — that was her name. She was one...