In response to the Air India disaster in 1985, where an unaccompanied bag contained a device, airlines became responsible for ensuring that in the event of a "no show" passenger, hold baggage that has been accepted from that passenger must not be allowed to travel on board the aircraft.
If an unaccompanied bag is accepted, it must be subject to rigorous security checks before acceptance. This process is referred to as Baggage Reconciliation.