Emotional = Captured
I tend to think this is a former LEO worker or CIA person who wants to inflict the maximum amount of hellfire on his/her former collegues and their families. These suburbs where sniping is going on are occupied by at least 75% government workers either directly or contracted. In some twisted sick thinking, such acts could be celebrated by many with beef's against our feds. I doubt they are emotional. Extremely angry? Pissed? Cause driven? Yes. Extremely disciplined? Yes. Likely to be caught? No. You will see an effort to round up the usual suspects though. This may continue on and off for years. Just when they arrest someone to satisfy the media you will see another shooting. Then another. Then another. And so on.
Other possibilites are that one of the murders was deliberate and the others were done to throw LE off the one that was intentional (pretty elaborate and risky scheme, but who said criminals were rational); and terrorists taking target practice in preparation for assassinations of major government figures (a lot of them live in Maryland). I don't think this is garden variety terrorism just being done for its own sake to scare people.