...The idea of a 21-year sentence for mass murder and terrorism may seem radically lenient in the United States, where life without parole is often presented as a humane alternative to the death penalty. Yet in testimony last week to a congressional task force on reforming the federal prison system, Marc Mauer, the director of the Sentencing Project, an advocacy group, suggested exactly that approach. He made the case for a 20-year cap on federal prison terms with an option for parole boards or judges to add more time if necessary to protect the public.
Such a policy would “control costs” in a system that is now 40 percent over capacity, Mauer told the task force, and would “bring the United States more in line with other industrialized nations.”
This proposal has little chance of becoming law. But a compelling case can be made for it nonetheless. Research by American social scientists shows that all but the most exceptional criminals, even violent ones, mature out of lawbreaking before middle age, meaning that long sentences do little to prevent crime.
Homicide and drug-arrest rates peak at age 19, according to the Bureau of Justice Statistics, while arrest rates for forcible rape peak at 18. Some crimes, such as vandalism, crest even earlier, at age 16, while arrest rates for forgery, fraud and embezzlement peak in the early 20s. For most of the crimes the F.B.I. tracks, more than half of all offenders will be arrested by the time they are 30.
And criminal careers do not last very long. Research by the criminologist Alfred Blumstein of Carnegie Mellon and colleagues has found that for the eight serious crimes closely tracked by the F.B.I. — murder, rape, robbery, aggravated assault, burglary, larceny-theft, arson and car theft — five to 10 years is the typical duration that adults commit these crimes, as measured by arrests.