We study the problem of forensic identification when the trace evidence fro
m the scene of the crime is imperfect: for example, it might be measured wi
th error, or be partially missing. A general framework for imperfect data i
s developed, and applied in particular to the following cases, singly and i
n combination: 'measurement error' in the recorded information at the scene
of the crime;'binning', i.e. discretisation of an originally continuous cr
ime measurement; 'paternity testing', in which the DNA profiles of the chil
d and of the mother provide partial information on the true father's DNA; t
wo types of 'laboratory error', one in which the error is equally distribut
ed among all possible results, and a second in which there is a bias in the
error mechanism producing a false match; and 'partial data', as when there
is information on the offender's DNA profile, but not on his racial group.