The government is yet to secure a high-profile conviction for graft.
Nigeria has recovered more than $500 million in cash and has seized over $9 billion in assets.
The British prime minister referred to Nigeria as "fantastically corrupt."
David Cameron referred to Nigeria and Afghanistan as "possibly the two most corrupt countries."
Ex-Nigerian ruler Sani Abacha is suspected to have looted up to $5 billion in public funds during his reign.