If he is not a governmental employee or is under an employment contract, then all employment in CO is considered "at will". What this means is that an employee can quit or an employer can fire or change the terms of employment (change hours, location, duties, etc.) at any time for any or no reason at all.
Wrongful termination only comes into play if you were terminated for being part of a protected class (gender, sexual orientation, age, disability, religion, national origin).
If he has done something that would be considered "misconduct" then they can not only fire him, but they can also deny unemployment benefits.
If they have evidence that a crime was committed, the employer can file a criminal complaint with the local DA. It would then be up to the DA to decide if there was enough evidence for him to pursue placing criminal charges against your son.
So the short answer is yes, they can terminate his employment for any reason and can file a criminal complaint and see if the DA will pursue it.
Assuming there is no other evidence and IF he fails a lie detector test for some reason, it is complicated and would be easy to see how they could trick him with questions.
In that case can the DA use a failed test as "evidence" to persue charges (if or where) there is no other evidence agains him?
Well, lie detector tests are not admissible in a criminal case. So unless they had some other evidence of wrongdoing, it would be hard for the DA to prosecute a case on "I think he did something wrong".
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