The two provisions invoked by the police serve different purposes in preventive policing.
Section 126: Security for keeping the peace
Section 126 of the BNSS allows an Executive Magistrate to initiate proceedings against a person when there is sufficient ground to believe that the person is likely to commit a breach of peace or disturb public tranquillity.
The magistrate can require the person to show cause why they should not be ordered to execute a bond, with or without sureties, to maintain peace. The period of such a bond cannot exceed one year.
The provision is preventive in nature. Its purpose is to address a potential threat to public order before a breach of peace occurs, rather than to punish a person for an offence already proved in court.
Section 170: Arrest to prevent a cognisable offence
Section 170 of the BNSS deals with preventive arrests by the police. It permits an arrest without a warrant when a police officer knows of a design to commit a cognisable offence and believes that the offence cannot otherwise be prevented.
The provision also places a limit on detention under this section. A person arrested under Section 170 cannot ordinarily be detained for more than 24 hours under that provision unless further detention is authorised under another applicable legal provision.
The invocation of these sections does not, by itself, establish that the three leaders committed a criminal offence. Their detention was preventive, and their release followed proceedings before the Executive Magistrate.