Based on the ethnicity of the suburban DC/Maryland immigrant communities (both legal and otherwise) the powers of logic then would tend to eliminate: Whites, African Americans and Native Americans. That leaves:
Asians
Hispanics
Middle Easterns.
It is hard to imagine an Asian doing this except perhaps Jemaah Islamiya from Indonesia or Abu Sayyef, or elsewhere. Also, I don't think the M-18 gangs from El Salvador or other vatos including homegrown gangbangers are doing this to the area, not to this level.
That leaves Middle Easterners.
And of course, we can't imagine any random terrorism against soft targets in the US by anyone from the Middle East, can we???? /sarc
All in All, Miss M and everyone, IMHO it's probably straight out of the Middle East. My best guess is Hamas-related, Iraq related or AQ related. My how they take the time to break the news slowly to the very source that can help them get the guy(s): The People!