Three, police instinct ought to be one of the criteria that police use to investigate crimes and determine their course of investigation. Four, it is a waste of limited resources to require the police, once they have developed a case against an individual (sufficient to meet the standards of the prosecuting attorney), to continue to investigate others on the chance that somebody else might be the actual perpetrator.As to part three, I don't have problems with an officer having a gut feeling. I just want the officer to have some sort of rational evidence of the crime he thinks has been committed (or will be in a Terry situation) before he can roust a citizen. In a street situation the officer often does not and therefore relies on tricks and technicalities which have been sanctioned by the courts (Whren &cetera).
In more serious cases the detective will often develop enough for a rational suspicion but if he relies on gut instinct may zero in on one of 4 people for whom he has rational bases for suspicion without evidence which would support an increased interest in that person. Ignoring potential evidence about the other suspects is called willful blindness. Willful blindness is usually found in the legal system when someone is asked to drive a car from point A to point B and given $500 to do so. In so doing he assumes liability for that of which he purposefully has no knowledge (usually drugs hidden somewhere in the car). Detectives are just as liable when they walk away from potential suspects because they choose not to pursue further evidence against them.
Still, a honest look at police activities would probably require some sort of sliding scale here. The wasted resources argument makes more sense for lower ranked felonies where we are only talking about probation or 6 months in jail (particularly in States where conviction does not result in the permanent loss of civil rights and where later proof of innocence can have a conviction removed). But as the felony charged becomes more serious this argument runs out of steam. I've discussed this in a somewhat different context here (the finality discussion). When the offense is larceny of a dog (a felony in Virginia) the detective is only going to devote so many resources to that case. When the accused is facing a potential life sentence or the death penalty "wasted resources" cannot be a valid excuse for willful blindness.
steve adds a further comment on people's awareness of what actually happens in the criminal justice system:
"[E]ven if more people were aware of just how sausage was made, they'd pretty much leave the process alone, warts and all.'The cheap shot here is to point to the "The Jungle" and how people cared deeply when they found out. But that really doesn't address his point.
There is no doubt that the majority of people in the system are guilty. More time is spent in courtrooms dealing with guilty pleas than anything else. If the system is seen in an overview it works properly the majority of the time. How much of a majority is impossible to know - Attorney General Ashcroft would probably say 99%; I would say maybe as high as 80%. And while perhaps 20% of my clients plead for reasons that are not related to guilt or innocence (usually to ensure their quick release from jail), most plea because the officer involved has done his job and gathered evidence such that my client is compelled to plead and accept responsibility.
However, that's not where our system ought to be measured. Our system must be measured by those cases which fall into the gray areas - those Defendants who ought to go to trial. By the time they reach the trial the momentum is just about to steamroll my client and the momentum begins when the detective goes to the magistrate and files the charge. If we do not, as a society and legal system, hold that detective to a requirement of investigating all viable suspects we countenance his abuse of the system because his personal prejudices.
The assumption that the system works, except for a few warts, and is the worst except for all others is extremely dangerous. In general, I agree that the adversarial system is better than the other , more common choice. However, that's not a reason to fail to hold our system accountable. There are very, very serious flaws in both the criminal justice systems I deal with (federal sentencing problems; Virginia jury problems). How do these flaws make it into the system? Because people don't pay attention and cave to the fear which is whipped up constantly over this evil or that (Anarchists, Communists, drug dealers, terrorists). Unless it applies to them most people do not favor Blackstone's ratio of 10 guilty freed rather than 1 innocent be convicted and would probably heap scorn on Ben Franklin's ratio of 100 guilty freed rather than 1 innocent be convicted. Thus our right to a fair criminal justice system which protects our rights has slowly faded and continues to do so.