It is not difficult to perceive why this should be so. After all, the typical person accused of a crime combines a troubled past with limited resources: he thus recognizes that, even if he is innocent, his chances of mounting an effective defense at trial may be modest at best. If his lawyer can obtain a plea bargain that will reduce his likely time in prison, he may find it “rational” to take the plea.
(a segment from “Why Innocent People Plead Guilty”, Jed S. Rakoff)
You should really go and read the whole essay from The New York Review of Books. Mr. Rakoff has been a prosecutor, a defense attorney, and is currently a judge. He offers some constructive solutions.
Being a believer in the rule of law and due process, and understanding law enforcement doesn’t always arrest the actual perpetrator, I have concerns about such a system. The Innocence Project (among others) has shown many folks arrested are cajoled/convinced/badgered into pleading guilty for a lesser sentence – even when they are not guilty of anything! As the police state agenda advances, I suspect his will continue.