But the client had made an offer of employment; then withdrew it because of the arrest record. Going SOLELY on that information (and I'm not convinced that we have the whole story) that would appear on the surface to be illegal. The EEOC has established that a policy of not hiring someone on the basis of an arrest which does not lead to a conviction can have an adverse impact on certain races.
However, if the poster had answered a question regarding arrests in an interview or on an application in the negative, perhaps believing that he was entitled under the law to do so (under Ohio law he's not, unless the arrest record has been expunged), then the employer would be entitled to withdraw the job offer not on the basis of the arrest record, but on the basis of his having lied. That is NOT illegal; in fact, I would expect an employer to do so. There could also be dozens of facts the poster has not provided which could change the situation.