Just look at homicides. A dead body is somewhat impossible to hide from the statistics. Then, overlay that data with any other category of crime. Here's a googl

Just look at homicides. A dead body is somewhat impossible to hide from the statistics. Then, overlay that data with any other category of crime. Here's a google image search: https://www.google.com/search?q=murder+assault+rates&rls=en&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiP8qbcppThAhUPyFkKHZT-B2sQ_AUIDygC&biw=1287&bih=826#imgrc=rSbHge7DGraf0M https://www.google.com/search?q=murder+assault+rates&rls=en&...: What you will see is broad agreements of the trends, often including fluctuation in shorter terms. Your theory would thus require (a) some evidence that the police is now somehow hiding murders, or (b) that murders fell but other crimes (even attempted murder) were somehow exempt from the trend and the police in almost any jurisdiction managed to underreport all other crimes with almost perfect accuracy to reproduce the trend in murders. The comparisons across jurisdictions is interesting by itself: falling levels of violent crimes have been observed across a broad swath across North America, Europe, and beyond. It's somewhat unlikely that all these unrelated police forces somehow simultaneously decided to and succeeded in embarking on a corrupt campaign to falsify statistics. If anything, the prevailing winds should have led to more crime being reported. Something like rape or assault tend to be taken more seriously these days. In cases such as Spain, one would also expect today's statistics to be more accurate than they were in the 70s, when it still was a fascist dictatorship interested in projecting an image of stability and safety.