Saint John the Evangelist Catholic Church cemetery in Silver Spring. It's on the grounds of land owned by Daniel Carroll, an historic figure himself and father of John Carroll, first Catholic archbishop in the U.S. (no, I'm not Catholic - just a history buff). Anyway, it was a beautiful day, and I've been meaning to wander the grounds, so did so. Oldest grave there that I saw was of Eleanor Carroll, wife of Daniel and mother of John, who was in her 90s when she died in the 1790s.
Anyway, I came across a small garden area with a little plaque giving the names and birthdates of Sheila and Katherine Lyon, who were 11 and 13 when, as the plaque indicated, they disappeared in April 1975.
When I got home I got online. I had no idea what a huge story this was in DC, one of the biggest ever - the Chandra Levy story of its time. And they have never solved it. Here's Wikipedia on this tragic story:
http://en.wikipedia.org/wiki/Lyon_sistersLike I said, haunting.