4 Any explosive device must contain some sort of timer and firing mechanism, as well as the actual explosive charge. I understand that military stores of Soviet Bloc origin, including timer/firing mechanisms, were widely available in Eastern Europe at the time of the incident. These mechanisms have a maximum delay time of not less than 24 hours and the firing time can normally be selected to the nearest minute, or at worst within five minutes, of a selected firing time.
5. The mechanism would also contain an arming pin or switch to be activated after the device was in place, thus ensuring the safety of the user. The Soviet Bloc electronic timer is about the shape and size of a packet of cigarettes, so it would have fitted quite easily into the shape and size of block being described.
Explosive charge and weight
6. The timer and firing mechanism can be surrounded by plastic explosive, moulded into a cube shape by hand, in exactly the same way as plasticene. Having allowed space for the magnet, the timer and the firing mechanism, the cube could certainly have contained one kilogram of plastic explosive and possibly as much as 2 kilograms. When referring to the possible weight of an explosive it is normal to refer to TNT equivalent. This is because effects of an explosion will not indicate exactly what type of explosive may have been used.
