The police have continually emphasized that the schools are safe since the beginning of the killing spree. Seems that the Evil SOB(s) involved here took a cue from this. As an ex-FBI profiler said today, the sniper is saying "In Your Face".
The LEOs need to start thinking of taking some novel, if not drastic measures. They have to focus more on anticipating the next likely targets, especially with respect to timing. Perhaps picking out say 10 prime areas in the DC area that would appeal to this Sicko (good cover/easy get away routes) and literally shut down all traffic with roadblocks and do a car to car search on everybody. Yes, it would take one helluva lot of cops to do this but it could trap the killers and flush em out in the open.