The Acting Comptroller-General of the Nigeria Immigration Service, Mrs Caroline Adepoju, has ordered an immediate investigation into the cause of an auto accident that killed at least four personnel of the service. Briefing journalists at the Service Headquarters in Abuja, on Monday, the NIS Public Relations Officer, Dr Dotun Aridegbe, said the CGI also declared three days of mourning even as flags will fly at half mast in all commands nationwide.