That's a reasonable question. Christianity does have an emphasis on forgiveness, which I suspect these prison chaplain programs emphasize - so it's more a matter of murderers turning themselves into Christians.
However murder is considered a mortal sin that separates one's soul from god and that cannot regularly be forgiven.
See https://en.wikipedia.org/wiki/Mortal_sin, scroll to 'Actions constituting grave matter' for the list.
My grandmother was devout and spent her last few weeks convinced she was going to hell for something I do not know.