The winning ticket for a $16.5 million lottery jackpot was turned in Thursday less than two hours before it expired, the head of the Iowa Lottery said.

Lottery officials tried for months to urge the winner to come forward and claim the prize. Iowa Lottery Chief Executive Terry Rich said the reminders “worked as we had hoped, and brought in the winner just in time.”

The identity of the Hot Lotto winner, and the story of why the winner waited so long to turn in the ticket, are still a mystery for now. Rich said the ticket was presented to the lottery Thursday by a representative of a Des Moines, Iowa, law firm on behalf of a trust.

“We look forward to learning the details we’ve all been wondering about these many months,” Rich said. “Every winner’s situation is different, and it’s always fun to hear the story.”

Until Thursday, all officials knew was that the $1 ticket was bought at a QuikTrip in Des Moines on Dec. 29, 2010. Odds of winning were 1 in 10.9 million, said Mary Neubauer, a spokeswoman for the state lottery.

The money will not be paid to the winner until the lottery can complete the standard security process for a jackpot win. Rich said additional security is now required because more than half the prize-claim period for the jackpot expired.

As the 4 p.m. Thursday deadline loomed, the Iowa Lottery received an increasing amount of calls, Neubauer said Wednesday night.

Some of the calls were from people who said they may have lost the ticket, or put it through a washing machine, she said. The callers are walked through a series of questions to determine whether they may indeed be the winner.

Other calls, she said, were from people who believe in the power of their own creativity. Once told they could not have been the winner, they would call back again and again, each time with a different story, she said.

The call from the law firm to claim the prize is not the first time a lawyer has come forward on behalf of a client about this jackpot, Rich said, but in none of the other cases did those involved have a winning ticket.

Another lottery winner wasn’t so lucky earlier this week. Monday, a $77 million lottery ticket went unclaimed in Georgia.

If the Iowa prize had gone unclaimed, the money would have returned to the 15 lotteries that offer the game, in proportion to the percentage of sales that came from each state. Rich said Iowa would have gotten back about $1.3 million, which they would have put into the prize pools for future games.

The Iowa winner will pay 25 percent in federal taxes and 5 percent in state taxes, Neubauer said.