Fig. 5-2-4-1 shows the repeat offender rate (rate of persons cleared who have previously cleared to all persons cleared) and the previously convicted person rate (rate of persons previously convicted of offenses other than Road Traffic Law violation to all persons cleared).
  As for homicide, among adult offenders, the repeat offender rate and the previously convicted person rate have been fluctuating within a range between 44.9% to 58.3% and a range between 35.3% to 50.4% respectively, declining slightly since 1987. Among juvenile offenders, it is difficult to identify a specific trend in the repeat offender rate because the number of persons cleared is so small and fluctuates significantly every year.
  As for robbery, among adult offenders, the repeat offender rate and the previously convicted person rate has been fluctuating within a range between 54.2% to 67.3% and a range between 40.8% to 52.6% respectively, remaining at a higher level than those for homicide but declining slightly since 1988. Among juvenile offenders, the repeat offender rate has been within a range from 49.6% to 63.4%, without showing a particular trend.
  Since 1985, among adult offenders, the repeat offender rate and the previously convicted person rate have been declining both for homicide and robbery, which indicates that homicide and robbery have been more frequently committed by persons without previous convictions or criminal histories.
  Such increase in the share of cases of heinous offenses such as homicide and robbery that are committed by persons without previous convictions or criminal histories suggests that heinous offenses are committed not only by repeat offenders and previously convicted persons who appear to have a criminal tendency but also by persons without previous convictions or criminal histories who do not appear or have not appeared to have such tendency.

Fig. 5-2-4-1 Trends in the previously convicted person rate (adult offenders) and repeat offender rate (adult/juvenile offenders) (1973-2002)