Investigators combing the site of the Boston Marathon bombings have recovered components of the two devices which killed three people and injured 176 others.
Together with analysis of numerous amateur videos they hope to provide answers to the all important questions – who set off the bombs and why?
As the city of Boston mourns the victims it is clear the makeshift bombs – two pressure cookers packed with nails and ball bearings and placed in innocent looking duffel bags – were meant to kill and maim.
One of those who died was eight-year-old Martin Richard who had been cheering on his father in the race. Both his mother and sister were severely injured.
The other two people who died were 29-year-old Krystle Campbell and a Chinese citizen whose identity was not being made public at the request of the victim’s family.