Old Cat and friends,pls help!

My friend had a legal problem recently. He worked in a company. Two months ago, for curious reason, he and his colleague (both were just came out of college) installed a spy software in office computer, which can access to administrative database. His colleague installed it and uninstalled it (but failed. That’s why company found it recently). My friend did discuss the technique issues with his co-worker, but he didn’t do it. Recently Company talked to both of them and my friend immediately confessed his role in this offence. But his co-worker told investigator it is my friend did it. So the company fired my friend and they reserve the right for further crime charge (they are evaluating the damage, but the Manager told my friend that preliminary report shows no damage happened). His co-worker got much less punished. In the early stage of investigation, my friend had a phone conversation with his co-worker, his co-worker admitted he installed the software and said some technique details, which my friend even doesn’t know. My friend recorded the whole conversation. As far as I know, this recording is illegal. So can he hand this recording to company? If not, how can he prove his fewer roles in this incident? He told me he deserved to be punished. But it looks like honest people got worse consequence than liar person.