The discovery of a child’s skeleton in a Late Neolithic well in Sweden raises again the issue of watery rituals and human sacrifice in prehistoric societies. Analysis of diatoms from the right humerus and from the surrounding sediment indicated that the child died by drowning and had not simply been disposed of in the well after death. The scenarios of accidental drowning and murder are examined to account for this discovery. The preferred hypothesis, based on a comparative study of similar finds from north-western Europe, interprets this instead as a ritual sacrifice. The use of diatom analysis to establish drowning as the cause of death adds a new weapon into the armoury of forensic archaeology.