They had been fiddling the accounts/books/finances for years.

Artwork by Katsushika Hokusai, "A merchant making up the account"

Word of the day
fiddle : to act dishonestly in order to get something for yourself, or to change something dishonestly, especially to your advantage

Quote of the day
“A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.”
― Robert A. Heinlein