We can not prove free will, but perhaps we can find suggestions for it.
Animals don't do it. Humans do it. Sometimes, for whatever reason, human beings end their own biological existences. Some do so not out of mental disorder, but for reasons of principle, rationally, with purpose. With will.
I'm talking about the Christian value of non-resistance, the ethic which teaches to put aside urges like pride, hate, revenge, violence, and teaches us to forgive those that wrong us, respond to violence with something other than retaliation, to love even our enemies. There is something in such an ethic that tends to go against both reason and biology. And yet it is.