RALEIGH, N.C. — The North Carolina Department of Instruction sent a letter to all public school systems on Friday -- the result of a fraud investigation involving the Wake County School System.

The letter demands all school systems have the proper checks and balances to catch fraud and prevent mismanagement.

Employees from Wake County Schools' Transportation Department are suspected of working with employees from a parts supplier to siphon millions of dollars of public money.

The department head and four other employees resigned. Two managers from Barnes Motor & Parts were fired.

Criminal charges are expected this summer.