What is distinctive about this is the frequency of the killings. Every day or every other day. Psychopaths of recent memory killed and then lay low for weeks or months before they struck again.
This is a concerted effort to sow panic and terror-specifically in the DC area. I wouldn't be surprised if the van is packed with explosives and the final end of this is a suicide mission. The cops will need to be real careful if and when they pull over the real perps.