Osaka police have admitted they did not report more than 81 000 offences over a period of several years in a desperate bid to clean up the region's woeful reputation for street crime.
The revelation came earlier this week when embarrassed authorities said they had kept the data out of national crime statistics between 2008 and 2012.
The deception, which amounted to nearly 10 percent of all crimes in the area during that period, meant that Tokyo appeared to have the worst national crime figures.
The vast majority of covered-up crimes were for theft - including tens of thousands of stolen vehicle and bicycle cases - but hundreds of more serious offences such as muggings and even murder may have been omitted from official crime data, the Asahi newspaper reported.
The force's top brass denied that they had ordered underlings to hide the data, and nearly 100 officers were reprimanded over the deception, they said.
But lower-ranking officers have told major media that authorities were under heavy pressure from a popular regional politician to change the city's image as a hotbed of criminality.
Internationally, Japan has one of the lowest crime rates in the world. But among ordinary Japanese, Osaka has long been seen as more dangerous than other major urban centres.
The commercial hub tends to live in the shadow of the bigger, more cosmopolitan Tokyo.
The hidden crimes were committed inside the city of Osaka, which has a population of 2.7 million, and surrounding communities.
The area had the dubious distinction of being Japan's most crime-ridden for the decade leading up to 2009. - Sapa-AFP