What is a safety critical system
A life-critical system or more commonly a safety-critical system is a system whose failure or malfunction may result in one (or more) of the following outcomes: death or serious injury to people. loss or severe damage to equipment/property.
But a more intuitive explanation may be
with the consequences of failure .If the failure of a system could lead to consequences that are determined to be unacceptable, then the system is safety-critical. In essence, a system is safety-critical when we depend on it for our well being. 
So does an investigation by the police constitute a safety critical system?
Despite it being rather counter intuitive, how can an investigation into a report of a crime that may have happened 10, 20 or more years ago, be safety critical and does it fit the into a reasonable definition of a system anyhow.
I would argue that yes it does meet both of these requirements.