Hello, I'm your neighbor on Quincy Pl. NW. I'm on the north side, sharing the alley with R St. NW, and I just observed the following:
A man (20's) with med-dark complexion and long braids (below shoulder blades) carrying a backpack just "perused" a vehicle on the alley. He peered in the driver's side window and tried the door. I saw him out my kitchen window, and immediately went outside. I asked if I could help him, and he replied "no." I asked him if he knew my neighbor, and he did not reply, but walked briskly away - westward down the alley.
Unfortunately you have to zoom in pretty far on my photo (I had to run inside to get the phone, by that point he was hurrying down the alley). He's thin, which makes him look taller, but probably 5'9" to 5'11" and wearing a beige/grayish sweatshirt, olive or gray pants, and a black backpack.
If anyone on the alley has security cameras, you might get a photo around 11:40am.