But corruption is a way of life. "Corruption" can be for personal gain, done out of theological or political zeal, done in exchange for protection or under duress, or paid as a kind of routine tax.
You are building something, you inflate what you need to be able to pay protection. Or your tithe.
If you're a wholesaler, you report a theft. You know who "stole" it--you provided the trucks--but you know those construction permits you applied for 3 months ago will be approved tomorrow.
You're a policeman and a theft is reported, you know the gangs in the area. You just don't bother to track them down until you know their merchandise has moved underground. (In Gaza, literally.)
Or if you're a local UN employee, you forget to report the theft. If the building material's then issued or even sold to somebody who doesn't actually exist, only a low-level audit that entails actually going out to visit the sites that materials were allegedly used in will discover that the building never happened.
Or you just skimp on construction, knowing that a small bribe or a bit of theological or political unity will provide the support that the absent building materials won't. Unless you actually measure the volume of concrete and x-raying to see if the construction iron's actually where it's supposed to be will find the problem. The only way you'll find problems is after the building collapses under its own weight or a bomb from the next Operation Crush Hamas levels a building that should easily have withstood the shock wave from 50 feet away.