Marathon Manhunt: No responsibility claimed, still no suspects in Boston bombing (VIDEO)

The twin bombs that killed 3 and injured more than 170 in Boston were reportedly homemade, and designed to maim as many people as possible.

Officials say there are still no suspects in what's the worst terror attack in the US since 9/11.

The tragedy took place at a major public event - despite years of tough, multi-billion dollar security measures.