In many nations around the world – particularly Britain and America – a 50-year overview of crime sees much the same kind of general trend:
A strong and consistent rise in crime 
from the 1980’s that peaks in the mid-1990’s and then generally falls over the next 25-years.
In England and Wales, for example, this is something that has been broadly demonstrated by both Official Crime Statistics and British Crime Surveys and new(ish) Home Office research suggests a possible explanation.
Nick Morgan’s (2014) “The heroin epidemic of the 1980s and 1990s and its effect on crime trends” looks at variety of UK crime trends and offers a useful – and short – overview of different kinds of sociological explanation (Economic explanations, Offender-based theories, Opportunity and security theories, such as routine activities, changes in the stolen goods market, and security improvements and Substance abuse theories) that both teachers and students will find useful.
The main interest here, however, is the claim that the generational fall in various types of crime is closely linked to changing patterns of drug use, with the rise and fall of heroin abuse being particularly pertinent as one explanation for falling crime.
It’s an interesting argument, albeit one you will probably need to precis before you present it to your students…