Google says "Definition of Liable: responsible by law; legally answerable".
If you claim he's not legally responsible but is "morally liable", where "liable" itself means "legally responsible", what in your world does the term "morally liable" mean, specifically? What does it mean you can do to him, or what does it mean you should do in future in response to this?
Google isn't the ultimate source of truth of the meaning of words. When someone says that another party is morally liable they mean morally responsible. That he ought to feel responsible and act according and consider others actions in the future lest he feel like he has morally failed people in the future. Ultimately we are often and are often expected to be our harshest critic and ought not to limit our duty to others to the minimum that the law requires.
Google says "Definition of Liable: responsible by law; legally answerable".
If you claim he's not legally responsible but is "morally liable", where "liable" itself means "legally responsible", what in your world does the term "morally liable" mean, specifically? What does it mean you can do to him, or what does it mean you should do in future in response to this?