First off, I'm sad your father in law got himself into this situation. I am a retired Illinois Conservation Police officer and have seen violations like this many times in my career. I am also an avid deer hunter and choose to hunt within the law. I doubt that the charges in Indiana are at the felony level but they could be. If your father in law is charged with a felony he should get a good lawyer. Felony charges will have a long term effect on his life.
As a sportsman I feel that by killing a deer outside the law, he has STOLEN that animal from the rest of us hunters that choose to obey the law. A quality hunt for a large buck may be valued at $5000 to $10,000. If a thief stole something valued at $5000 to $10,000 from your father in law I'm sure he would want the thief prosecuted to the fullest extent of the law. Just an opinion from an old game warden.