Sign up for a free trial of News Direct's animated news graphics at http://newsdirect.nma.com.tw/Reuters.... For story suggestions please contact [email protected] Investigators piecing together evidence from the scene of the Boston marathon bombings believe the twin devices were triggered using electronics from toy cars. The pressure cooker bombs were concealed in bags. The devices used radio controlled car components, including a 2.4 GHz radio receiver, an electronic speed control for the trigger and a sub-C rechargeable battery pack. The bombs were packed with Nitrate and perchlorate oxidisers, allegedly taken from fireworks and ball bearings and carpenter's nails that served as shrapnel. The air-tight pressure cooker allowed the slow-burning explosive to generate lethal force. A New Hampshire pyrotechnics firm said the elder brother paid cash for $200 worth of 'lock-and-load' fireworks kits. Such kits are not legally available in Massachusetts.