[D]riven by tougher laws and political pressure on governors and parole boards, thousands of lifers are going into prisons each year, and in many states only a few are ever coming out, even in cases where judges and prosecutors did not intend to put them away forever.

Indeed, in just the last 30 years, the United States has created something never before seen in its history and unheard of around the globe: a booming population of prisoners whose only way out of prison is likely to be inside a coffin.

As a punishment, life without parole is preferable to death, which ends the opportunity to correct an erroneous conviction. But life sentences have too frequently been imposed under "three (or two) strikes" laws for conduct that doesn't warrant a permanent loss of liberty.

Fewer than two-thirds of the 70,000 people sentenced to life from 1988 to 2001 are in for murder, the Times analysis found. Other lifers - more than 25,000 of them - were convicted of crimes like rape, kidnapping, armed robbery, assault, extortion, burglary and arson. People convicted of drug trafficking account for 16 percent of all lifers.

Parole boards can keep the dangerous and incorrigible imprisoned while permitting those who pose no social threat, and those who have been punished enough, from wasting prison resources. Parole boards serve as a post-sentencing corrective that is desperately missed in sentencing systems (like the federal system) that have abolished parole.