Isn't easy? Try "impossible". Not because there is no reasonable explanation, but because the feeding frenzy attacking him will accept no explanation. Most members of that mob come across to me as abysmally ignorant, insufferably arrogant, and completely irrational.
His best bet would be to tell the mob to fxxx off. It's all they deserve. It won't do any good, but it's better than groveling.
You didn't answer my question. Is they anything he could say that you, personally, would find a satisfactory explanation?
I honestly don't know.
Right now, it seems that he probably wanted to put a lion's head on his wall because he thought that the trophy might somehow bolster his image as a man - that it might make him seem more masculine than he thinks people are viewing him now. I think he was hoping that people who see the trophy might think that he had earned it by engaging in acts of personal courage by challenging and defeating a dangerous predator. You know, there are people who buy and wear service medals that they didn't earn. People do a lot of weird things for a lot of weird reasons. Traveling halfway around the world to kill a defenseless lion seems so pointless, so gratuitous. But, he must have had some kind of reason.
Anyway, his actual motives might be completely different. Maybe he just hates animals.
That's why I think he should come forward to explain why he was doing what he was doing. His silence is inviting other people to attach to him motives which may be unfair.