Arrest and detention on grounds of suspicion rather than factual evidence may follow from a suspension of habeas corpus on the declaration of a state of national emergency. Internment without trial may be justified by the authorities as being necessary in a state of war or guerrilla or terrorist attacks or in an extreme strike situation, but may equally be used to suppress legitimate political opposition and human rights. If internment is on a large or sophisticated level, concentration camps may be set up and torture used in order to obtain confessions.
An individual may, in various circumstances, be arrested in certain countries without being given any grounds for such arrest. There have been cases of arrest on grounds which, in their very wording, seem to constitute violations of human rights; or on the basis of charges so vaguely framed that they could easily serve as a pretext for violations of human rights. Persons may be arrested for having expressed, in a non-violent manner, their political, philosophical or religious opinions; the purpose is to forestall any attempt to oppose a regime. In view of the policy of secrecy practised by various governments on the alleged basis of public security requirements, it is often difficult to obtain information on the identity and the number of persons thus detained, precisely because of the absence of charges and of reports of proceedings.
The two main laws permitting preventive detention in India permit up to one year's detention without trial or charge.
In 1990, there was said to be many thousands of people in long-term detention outside the legal system in China. The requirement by law to notify the detainee's family or work unit within 24 hours of his/her arrest has been systematically ignored. Torture and ill-treatment of detainees was said to be commonly practised. In 1993, internal Chinese police reports indicated that about one million people are detained annually for up to three months, a form of routine social control called "shelter and investigation". They include the mentally ill, workers who "violate labour discipline", vagrants, peasants protesting against high taxes, couples infringing family planning rules, those belonging to religious sects, and petty criminals. Many students and worker arrested after the Tiananmen Square massacre (Beijing, 1989) were held under "administrative regulations" for weeks or months without being tried. These procedures have also been used to detain demonstrators in Tibet.
In some countries deprivation of liberty is lawful if a person is considered a risk to society, or to certain interests of the State, without him having committed a criminal offence.