The ticket was legitimately purchased but officials cannot confirm by whom, USA Today reported.
Attorney Crawford Shaw, representing a group named Hexham Investments Trust, claimed the prize in December, 2 hours before the one-year deadline expired, but withdrew the claim on Thursday.
Shaw says even he does not know who is behind the ticket purchase, although he mentioned to the Iowa Lottery his client is from Belize.
Lottery officials said no prize would be awarded unless the purchaser's name can be disclosed, the Des Moines Register reported.
The Iowa Attorney General's Office and the Division of Criminal Investigation are looking into the matter but lottery officials said there was no evidence of illegal activity, only a frustrating lack of information.