The acquisition of breaking and broken glass

A set of experiments tested the idea that an examiner can distinguish glass acquired by backward fragmentation from that acquired by contact with already-broken glass. A window was broken. The exterior surface of the breaker's clothing was brushed and hair-combings taken and these were searched for glass fragments. Wearing the same clothing the breaker then cleared up the broken glass and further hair-combings and brushings of the clothing surface were taken. The size, shape and presence or absence of an original flat surface was recorded for the recovered fragments. The distributions within these parameters were compared for the two methods of acquisition and association between the method and the parameters was tested using contingency tables. It was found that fragment shape does not identify the method of acquisition and that a high proportion of fragments retaining the original outer surface shows that the glass was acquired by backward fragmentation.