Depending on the context, one can use various definitions. First of all, one should understand whether mentioning a person's citizenship has any added value. In the same way, there is no need in mentioning the nationality of a person in a crime report. If it is necessary, depending on a status, you can write the following:
A refugee or an asylum seeker, if a person had or applied for the refugee status;
A foreigner or a foreign citizen;
An undocumented migrant. Try to use this expression, if you have to mention a person's documental status, but this information is rarely necessary;
A person who is suspected of violation of migration legislation or commission of an administrative offence – this is the most correct and humane definition.