“I am very pleased to offer you the full-time position of Senior Analyst, Security Compliance,” - so why doesn't he take that job? Or are they offering him the job and then by the time he goes to take it they've googled him and changed their minds?
Even though he was exonerated, his prison stay and other convictions may show up. He can explain, but a firm can rescind an offer for whatever reason they want (outside of protected statuses, which does not include criminal background). For a security position firms may want perfectly clean backgrounds.