It Fell

Mark worked two jobs as a security guard in Cleveland, Ohio. He was walking outside the downtown building where he works at 7:45 a.m., when three 42-pound bundles of money fell out of an armored truck en route from the Federal Reserve Bank to Jacobs Field, home of the Cleveland Indians baseball team.
 
The back door of the truck apparently was left ajar. Inside the bundles wrapped in plastic was a total of $646,000 in cash. Mark turned in the money to the FBI two days later.
 
The FBI reportedly told him, Youre not getting a reward and youre lucky youre not going to jail, suspecting that Mark had planned to keep the money until he thought that some of the money contained marked bills. Mark said, I froze for maybe a second, when he first saw the money, but his two-day wait to return the money was caused by trying to figure out how to claim the $75,000 reward offered for the moneys return.45
 
Was Mark morally obligated to return the money?
Should Mark be penalized for waiting two days to return the money?
What would you have done in this situation?