Investigations into PSERS have cost the teachers’ pension plan $4.5 million in legal and adviser bills since March 2021, state records show. That’s enough to pay 170 retirees the average pension of $26,000 for a year. The system invests $75 billion for half a million working and retired members, at a cost to taxpayers of $5 billion a year, and another $1 billion from school staff payroll deductions. Investment profits also contribute to PSERS. The bills are piling up as trustees of the system, known as the Public School Employees’ Retirement System, are under two federal investigations and are…