the A&S Museum downtown will keep you busy all day, and keep you downtown, where all of the good stuff is...
Crime is everywhere, not just DC. Don't run around scared, but be cautious. I drove to AZ last week, and on the way stopped at a rest stop to relieve myself. I was out of the car for maybe 3 minutes, but had left the drivers door unlocked. OOPS, I lost my camera bag, with my Canon EOS Elan, with 3 lenses, my new, Canon Digital Rebel camera, (which uses those lenses, also), my, almost-new JVC digital camcorder, and a great pair of Nikon binoculars. The $$$ weren't as much a loss to me as the exposed fim, and the 4 videotapes in there, with my Grandson' birth, and 1st birthdays, and my granddaughters' Christmas. (if anyone sees my stuff, with a black nylon bagf, I offer a $1000 reward)
Keep aware!
Wow - you learned the hard way. These days, you need to ALWAYS lock your car, not only when you get out, but when you get IN. That's the first thing I do, even in broad daylight. Carjackings have become a common occurrence, and not just in large cities :-(