Boston on High Alert After Bombing

Investigation ongoing

Authorities studied surveillance video, combed through debris and flooded the streets with investigators Tuesday in a rush to determine who set off two shrapnel-studded bombs at the Boston Marathon that killed three people and injured at least 144.

Law enforcement officials searched a suburban Boston apartment building, interviewed a man and removed a duffel bag and two trash bags overnight. They also issued alerts for a rental van and a man seen leaving the scene of the blasts.