Helping my dad

My Dad ALWAYS goes out of his way to help people when they are in need of things...ALWAYS has and Always will.. But he is 84 years old and this past Saturday during a 25th wedding anniversary for my wife and i at his house...1 of our guest FELT THE NEED to STEAL 500.00 in cash from his desk drawer and nor he or I didnt realize it til Monday..I have an idea of who did it but i have NO Proof...Im asking you to PLEASE HELP ME TO GIVE BACK TO HIM... Like i said he loves to help people and Now i want to help him....Thank You in Advance