Why don't police ask the obvious questions before arresting someone?

why are police so impatient about arresting someone and then fail to take them to a magistrate before releasing them from custody? This is clearly a due process right at least in Virginia. Instead of being examined under oath by a magistrate, they choose to interrogate the suspect, and without giving them a clue as to what is going on, and search without a warrant. Police routinely deprive people of their rights, and it seems to me that if that followed this law that many many problems could be avoided. Its obvious that they don't want to be charged with false arrest or search w/o warrant by the magistrate, but if they were really concerned about that, then why don't they consider questioning the suspect about what they are doing, and before arresting? Why don't they question the word of the suspects accuser? When the police start an investigation, they seem to get too focused on one person and they never stop to think that maybe the person making the accusation doesn't know squat about what they are saying?