According to court records, a dozen current and former principals in the Detroit public school system have been charged with bribery.

The extent of the charges are expected to be announced later Tuesday during a news conference held by the U.S. Attorney’s Office.

The Detroit Free Press reported that as the city continues to dive in to school corruption, the federal government launched a “legal bomb” targeting current and former administrators and one vendor. The charges stem from a nearly $1 million bribery and kickback scheme involving school supplies that were rarely ever delivered to students.

Norman Shy, owner of Allstate Sales was charged with paying over $900,000 in kickbacks to at least 12 DPS principals who used him as a school supply vendor in exchange for money.

Shy allegedly ran the scheme for five years with the help of Clara Flowers, an assistant superintendent of DPS’s Office of Specialized Student Services. The scheme worked as follows:

The principals would certify and submit phony invoices to DPS for the school supplies. Shy got paid, but the goods were rarely delivered, only sometimes “for the purpose of making the transaction paper legitimate.”

Shy maintained a ledger to keep track of how much money he owed Flowers in kickbacks, which came in the form of cash and gift cards. The two regularly met to discuss how much Flowers was owed for her favors. Shy was careful not to get caught, disguising his payments to Flowers in a variety of methods, such as checks payable to contractors, including a painting and gutter company, who worked on Flowers’ home. Shy also used DPS money to help pay for a new roof on Flowers’ house.

The sting comes only two months after ex-principal Kenyatta Wilbourn Snapp admitted to pocketing over $50,000 from a vendor to spend on personal interests while working for the Education Achievement Authority, an agency with aim to help Detroit’s most troubled schools.

Snapp is currently facing 46 months in prison.