Let me ask you this Scorza, the police don't have the full facts and can only go by what is presented to them at the scene , so going by your logic it would also have been wrong to arrest the gang of youths, right?
No, because the facts at the scene of the crime (i.e. vandalised van, badly beaten homeowner's son, homeowner's coherent statement, five known trouble-makers present with no valid reason and involved in a scuffle) are enough to suspect the youths of those charges.