The analogy really doesn't work. As a police officer, I don't serve the business owner. I serve society. Both the employee and the con man conspired to violate the laws of society. I would arrest them both and if the business owner interfered, I'd arrest him/her, too.
Now, the business owner does have a relationship with the employee that he does not have with the con man. The owner can't fire the con man. The owner doesn't have to have evidence beyond a reasonable doubt to punish the employee. The employer doesn't even have to incur a loss to fire the employee. The main difference between the con man and the employee is one violated the trust of the employer.
The employer never placed any trust in the con man. The con man never had access to steal from the employer. The con man can repay the money stolen and agree to never come into the store again. The con man and the employer would be restored to their original status (two people who don't really know each other and don't particular trust each other).
The employee and the employer can't just kiss and make up. The employee can't just repay the money and be restored to the original relationship. The employer will have to conduct an audit because he can't trust any transaction his employee ever made. Any advise or recommendation ever made by the employee will be suspect.
In an adultery, there is more than just a sexual violation. The OM/OW's violation was taking sexual rights legitimately belonging to the spouse. The married partner's violation was vastly compounded and so was the damage. There were series of lies and deceptions, violations of intimacy, massive violations of trust. You were not just a sexual partner with this person but a financial partner, a child-rearing partner, a future planning partner, a property owning partner, secret sharing partner, etc. You were none of those things with the OM/OW. Without the complicity of your spouse, the OM/OW had no power to harm you. Considered in this light, the OM/OW hasn't really harmed you, because the door to your marriage was guarded by your spouse. If your spouse wishes to cheat, does it matter who the OM/OW is or even how many OM/OW there were?
Now, if the OM/OW also had a position of trust with you (a family member, close friend, employer, co-worker, etc), then their violation of you was compounded, but the violation caused by your spouse will always be the greatest.
There is a third person who deserves some share of guilt in an adultery. That is the "victim" spouse. They willingly married a person who would cheat. They failed to guard the relationship.
In your analogy, the employer bears some responsibility. He hired a dishonest employee. Maybe he should have conducted a better background check. He helped create conditions where his employee believed his crimes would go undetected. Maybe he failed to adequately compensate or show appreciation for the employee, thereby giving the employee little reason to remain faithful.
Of the three, the employer can only really fix himself. He has some influence over the employee (if he permits the criminal to remain employed). He has no real influence over the con man. There would be little value in outing the con man because anyone who knows the con man has already figured out he's dishonest. Being a con man, he likely cares little about what others think.