Criminal investigators aka Crime Scene Investigators (CSI) do not work a typical 40 hour week. The hours per week a CSI works depends on a number of factors, including location and demand.
CSI's working in small cities or rural areas are not likely to experience the fast pace and demand of those working in large cities with higher crime per capita.
Generally speaking, CSI's work long hours and must be available to work nights, weekends and holidays.
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Investigators do the interviewing of witnesses and suspects, develop and follow leads, etc. So there is a difference.