Thank you for your reply.
Unlike a police investigation, where you have rights, you as an at will employee do not have such rights when it comes to answering employer questions about your employment. Refusal to answer an employer's questions about your job is considered insubordination and grounds for suspension or termination
I am afraid. He did not have any duty to tell you about his investigations, he had the right to ask questions and as an at will employee you had to answer any questions asked about your employment.
NOW, the comment you stated above about them not thinking someone like you would be looking out for the store, is potentially evidence that they targeted you based ONLY on your age/race/sex/disability/national origin, and if they did so that is unlawful and considered discrimination
and harassment. If you can show that they were thinking you were a thief based on your age/race/sex/disability/national origin, then you have a basis for a discrimination claim and you would have to file a complaint with the EEOC
as they have to issue a right to sue letter for you to go to court. The statement that you said was made above would be your support that the only reason you were targeted was for your appearance, if that was based on age/race/sex/disability/national origin and that would be your only real basis for a legal claim against the employer.