The decline of criminal energy with growing age in the general offender population is replicated in a similar pattern for the active and serious criminals. Predictions of their dangerousness can be made more accurate by using longitudinal statistics on re-offending according to age, crime type and previous convictions as base rates. For this purpose Blumstein and Larson (1971) conceived a model of the interactions between offenders and the Criminal Justice System. It can be used to calculate the average number of offenses committed by a given type of offender such as street criminals or sex offenders after release from long prison sentences. As a consequence of the aging-out effect the number of offenses will considerably reduced after several years behind the walls, even for those ex-convicts who were not able or not willing to benefit from rehabilitation programs.