Japan saw a record number of child pornography cases last year, reflecting a crackdown made possible when police acquired a massive list of child porn buyers that included teachers and politicians.

A National Police Agency report released earlier this month said police arrested or referred to prosecutors 1,703 people involved in a record 2,413 cases, up 316 from the year before.

“Japan’s child pornography issue is notorious worldwide,” a senior investigator said. “Because there is demand, there are victims, so we need to thoroughly clamp down on the crime.”

There were 201 cases involving possession of child pornography, nearly triple the number from the year before, while production rose about 10 percent to 1,414 cases. Cases of provision and public display of such material remained almost unchanged at 798.

Behind the leap in possession cases were investigations launched following the arrest by Tokyo police of four people last May over suspected sales of child porn DVDs on a membership website.

While analyzing data left on computers confiscated in house searches, investigators discovered a list of some 7,000 purchasers, one of the largest such lists ever found in Japan, that included names, email addresses and titles of DVDs they bought.

But what the police learned through later investigations has more serious implications than the large figures.

They discovered that the buyers included people who were routinely involved with children, such as elementary school teachers and preparatory school managers, and public figures such as municipal assembly members, prefectural government officials and even police officers, showing the deep and wide extent of child pornography in Japan.

The list enabled investigators to track down the purchasers because the seller had them pick up the DVDs at post offices rather than receive them at home and risk being discovered by family members.

The purchasers had to provide identification when collecting the packages at post offices, which helped the police track them down.

While crimes unveiled through the list may just scratch the surface, the officer said investigations based on the list were significant as they have “rung the warning bell that child pornography itself is wrong.”

The Tokyo police judged that around 2,700 of the 7,000 people on the list can be referred to prosecutors and have provided the details to police in other prefectures. Investigations into the cases picked up speed starting last autumn and have led to the arrest of over 200 people so far.

However, future police work may not discover such large lists of purchasers as people are more apt to communicate through social networking services, often using a closed network for sharing images, without involving outsiders like DVD retailers.

The NPA report said 42.4 percent of the cases involved children coerced or tricked into sending nude selfies taken with smartphones, making it the single most common method for obtaining photographs.