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Criminals are well aware that making a phone call leaves a trace behind, which might later be used by police, and later still, in court. Therefore they will often switch phones, and preferably use more or less anonymous phones for "business". However, at the same time as they are using one phone for their work activities, they are possibly using another phone for legitimate business or for ordinary private purposes. This leads to the phenomenon called "co-location": two mobile phones apparently moving together, each separately making calls, but as if the two phones are in the same hands.
How can one find phones, and then co-locating phones, associated with some crime? Can one decide from a short history of apparent co-location whether or not the two phones were in the same hands? How strong is the weight of the evidence in discriminating between two hypotheses: the phones colocate by chance (defence hypothesis) or they colocate because they are in the same hands (prosecution hypothesis)? We have to distinguish two phases of "research": exploratory (criminal investigation) and confirmatory (criminal prosecution). I discuss the roles of statistics in these two phases of forensic statistical analysis of mobile phone co-location.