The march was then subjected to a baton-charge by the police, prompting the leader of the state opposition to claim that "democracy was being killed".
The fourth boy, a resident of Raza Bazar, surrendered earlier on Friday at the chief judicial magistrate court here.
Efforts are also on to ascertain the identities of all the accused allegedly involved in the crime.
A CBI inquiry was ordered into the Muzaffarpur case while the police was probing others.
The police are still looking for the fifth boy, who is said to be the son of an influential man.
The boys had access to mobile phones as they were attending online classes.