A police liaison is a function or role which can play an important part of a large security apparatus. You’ll often find that security guards will have training in this area, so that they know precisely how to use and supplement the efforts of police.

The kind of things that a police liaison will be expected to do and know is, obviously, laws on protection of property, apprehending criminals (as a private citizen), in-house police regulations and policies, as well as having personal connections with police personnel. When the scale of a police operation reaches a certain size, you’ll often find that the role of a police liaison is brought down to a specific individual to take responsibility of, which is done in a effort to increase effectiveness.

These roles are necessary for places which regularly see high security risks, particularly when those security risks are of a level of seriousness and maliciousness. So think less retail store apprehending the occasional shoplifter and more a security detail working at important places for national infrastructure, like the national grid, power generation centres (nuclear power stations etc) and airports.