I tend to lean towards the terrorist explanation (on a poll on www.courttv.com early this morning only 30% felt it was a case of terrorism.)
It could also be members of Hispanic gangs active in the DC area, perhaps part of initiation into the superviolent Salvadorean MS-13 which has chapters across the country. Or one of the many Asian gangs active in the DC area. So far no Asian victims.
It could be also some crazy cult members, such as surviving member of Rev. Jim Jones's Death Squad. Jones used to scream "I am God." The black cult leader, Father Divine, likewise declared himself as God.
Cab driver from India.