To apprehend someone is to catch or arrest someone suspected of a crime.
Apprehend is a term used almost exclusively in the criminal law. For example, in the international criminal law context you might hear political leaders saying: “the suspected terrorists will be apprehended and brought to justice”. So, in this context the meaning is that they will be caught and put on trial.
Note that technically an arrest (or apprehension) takes place when a person is actually stopped by the police or some other actor with legal authority to do so. In this case, what is meant is simply that the person has been deprived of his/her personal liberty i.e., they cannot continue on their way but most stay with the policy until they are released.