Why the practice of "plea-bargaining" exists
While the people of the United States pretend to cherish the procedural rights of the accused in criminal cases, the majority are never willing to pay for those rights to be fully exercised. Legislatures love to make things illegal, and demonstrate their resolve by prescribing ever-more lengthy punishments, without a concommitant provision of resources for enforcement. There is no way that all conduct which has been declared a "crime" could be investigated and subjected to a full jury trial, and there are not enough jails to hold all the people who could be convicted if everyone got the maximum sentence.
The institutional solution has been plea-bargaining: the offer of a reduced or even suspended punishment in exchange for a plea of "guilty" by the defendant.
Prior to the 19th century, plea bargaining was rare, but it did happen, particularly in high profile cases. In 1633, for example, the astronomer Galileo accepted house arrest from the Inquisition in exchange for reciting penitential psalms weekly and recanting the heresy of Copernicus. The Inquisition did not lack the resources to try Galileo and have him burnt at the stake, but the political will for the maximum sentence may have been lacking, and getting Galileo to recant was sufficient to send a "message" still reverberating through history.
The explosion of civil litigation in the 19th Century, which in turn can be attributed to industrialization and the creation of a middle class, created an enormous burden for Anglo-American judicial systems. Simultaneously, there developed a tendency to "criminalize" behavior which had heretofore gone unpunished or simply had not occurred. Only with industrialized standards of living did it become a crime to operate a pig farm in the wrong "zone", to sell spoiled meat, to engage in "insider trading" or to exhibit obscene films outdoors. Enforcing all these laws does not come cheap, especially using a system which guarantees expensive procedures like a jury trial.
Some object to plea-bargaining on the grounds that it allows criminals to "get away" with lighter sentences, but in fact, that would only be the case if every District Attorney had unlimited resources to investigate and try cases, which is not at all the case. In fact, if every defendant refused to bargain and forced the issue, the typical District Attorney could not prevail in most cases, or even half of them. Eliminating plea bargaining thus might bring the conviction rate down to 50%, given the limited resources and time to bring every case to trial. With plea-bargaining, almost every District Attorney in the United States can sustain conviction rates in excess of 90%. Thus, plea bargaining results in substantially more convictions, albeit with slightly reduced sentences, but with the expenditure of a lot less money.
In fact, the system has such coercive power that some defense experts contend it compels many innocent persons to "cop a plea" to avoid a more serious, erroneous sentence, including but not limited to wrongful execution. One example is the Central Park Jogger Case, where offers of lighter sentences convinced five youths to confess to a rape which they didn't commit.
How it works
When you plead "guilty", you are not merely admitting guilt. You admit guilt and specifically waive three important Constitutional rights:
- the privilege against self-incrimination;
- the right to a jury trial;
- the right to confront one's accusers.
You also waive all objections to the manner in which you were arrested and the manner in which evidence was gathered against you. A "no contest" plea is a waiver of all those rights without specifically admitting guilt.
Pleading "guilty" or "nolo contendre" (no contest) is therefore a significant concession. In the United States it is entirely possible that a defendant may be "caught red-handed" and yet go free. The usual reason for this is the "exclusionary rule", whereby a judge excludes from trial any evidence obtained by police misconduct, in violation of the Fourth Amendment. Other kinds of misconduct can also result in crime going unpunished: failure to bring the case to trial promptly (in violation of the Sixth Amendment), failure of the prosecution to ensure the attendance of witness against the accused (also a violation of the Sixth Amendment, which guarantees the accused the right to "confront" the witnesses against him). In ordinary traffic cases, the most frequent reason a violator goes free is that the police officer who issued the ticket fails to show up for trial. In the American system, this results in immediate dissmissal of the charges.
On the other hand, a plea of "not guilty" is not testimony, and does not waive the Fifth Amendment privilege against self-incrimination. While normally any testimony by the defendant, no matter how brief, opens the door to questioning by the prosecutor and being compelled to answer, a "plea" doesn't count as an attempt by the defendant to deny guilt. Regardless of the words used, "not guilty" really constitutes an announcement to the judge that the prosecution and defense have reached no agreement and the defendant insists on his right to trial.