@OmSigDAVID,
Sorry but it doesn't work that way.
In our society the individual member doesn't get to decide when the government has defaulted on its criminal justice obligation, anymore than they get to decide if they are in fact a victim and that a certain party deserves punishment.
If you, and a thousand others, watch a man brutally kill your wife on a crowded NYC street, chances are excellent that you are quite capable of accurately determining where guilt lies, and may even come up with a punishment that your fellow citizens agree is appropriate
(Let's stipulate for the sake of this hypothetical that you were incapacitated at the time of the murder and so were unable to draw your gun and either save your wife or deliver swift justice to her murderer
)
It is far less likely however, that the State will default on its obligation and forget about the crime.
A more likely scenario which demonstrates why in a society based on the rule of law, there are no exemptions, is that you are walking down the street and a vehicle jumps the curb, striking and killing your wife. The driver of the vehicle turns back onto the road and speeds off, never stopping and never reporting the incident to the police. You believe you know who the driver is and tell the police. The police conduct a shoddy investigation, but in the end don't have enough evidence for the DA to bring charges against the man you are certain killed your wife.
In your mind the State has defaulted on its obligation and the duty to avenge your wife reverts to you. You go to the man's house and when he responds to your knocking by opening the door, you shoot him dead (or, in the alternative, you beat the hell out of him or imprison him in your basement for 35 years). Maybe he was the guy, and maybe he wasn't, but in your mind justice has been served and the victim avenged.
If the state is incapable of infallible prosecutions, how much less so are its citizens?
Of course you can always act outside of the limits of the laws which you have agreed to follow as your part of the bargain, and take justice in your own hands when you are the convinced the State has dropped it. You will, of course, be subject to prosecution and punishment by the State, and this time they will almost assuredly not drop the ball.
Now we all know that you would
never punish a man for a crime he didn't commit, but we can't say the same for some 300 million other Americans.
There aren't any circumstances or systems under which justice will always be perfectly applied, and you or I may, unfortunately, be victims in a case where justice is incompetently pursued or not even pursued at all. That
is the way it works.
