Police on Wednesday turned over to prosecutors their case against four managers of a Saitama designer school who are suspected of illegally issuing inflated class-attendance certificates to foreign students so they can remain in Japan to continue their nonpermitted work outside school.

According to the Metropolitan Police Department, the four, including the president of the school in Omiya, allegedly violated immigration laws by assisting students from China and Bangladesh, who never attended classes, to renew their student visas and continue their work at restaurants by issuing bogus certificates last year.

Foreign students are allowed to work up to 28 hours a week, but many students at the Omiya school exceeded the limit to work 300 hours a month, or some 75 hours a week, the MPD said.

In exchange for giving favors, the school collected "fees" from each student — ¥1,000 for two days of bogus attendance — the police said.

The head of the school reportedly told police he wanted to sustain the school, where the number of Japanese students has radically dropped in recent years. Currently, its 160 students are all foreigners.