Immigration proceedings are usually administrative, this is why people often proclaim that visa violations are as same as parking violations. So there is no need to charge as there is no trial and there is administrative detention among the punishments. On the same note, "immigration judge" is not a member of the Judiciary but an officer of the Executive branch and "immigration court" is an Executive office as same as DMV.

There are criminal charges possible but are not necessary to indefinitely detain and/or deport any non-citizen who appeared on the border.