This guy either was too much of a newb to figure out how to mix the coins or assumed he had all his bases covered in terms of thinking his actions were beyond an investigative protocol. Now, he just blew his career and screwed his family over, both financially and in shame.
I don't think so, even a 15 years old tech savvy kid knows how to mix coins. The agent probably knew that the Feds will find out about his theft and decided to rather turn himself so his sentence will be reduced. Tax dodgers do the same so they have to pay smaller fines.