Again, why is it so obvious to you that they should be arrested for a crime before it has even been established that a crime has occurred?
A crime has been committed, someone has been stabbed to death. Do you think no murdered should be arrested till after the court appearance. How do the police know they where burglars, how do they not know it was gang warfare or any other number of possibilities. They have to be arrested so they can be cautioned and questioned. It really is utterly retarded to say they shouldn't be.