Having had dealings with several Nigerian Government officials over the years, I can tell you for sure that they all squirrel their ill-gotten gains in the Western banks from the moment the word Procurement is uttered. If there's any money in Nigeria, it's in obsolete European currency or something not negociable, like roubles or kuna. I've heard of people getting deaded and physically damaged through these scams.
My dealings have been in exporting goods to Africa. It's not unusual for people exporting goods to Nigeria to disguise them by packing the cases out with old magazines, and sending full cases of magazines as a decoy - then declaring the full shipment as medicines - this is to discourage outright theft. The customs ignore it, presuming that the importer's scam is to pretend to import medicines, then supply counterfeit medicines. Sometimes the medicines actually get to the man who is paying for them, if there's enough magazines to cover them.
When it comes to paying money out for imported goods, those who have it tend to appear at the dockside agent's office with plastic carrier bags stuffed with miscellaneous foreign cash - they don't keep money in the bank, because the bankers are as bent as the politicians.