This could also be said for Judas,
for Peter,
Pope Formosus,
Calvin,
Luther,
For John Wesley, Napolean,
Hitler, or even for Elsie.
What we CAN do, is look at the history of these individuals and see if it’s likely they changed their minds and hearts at death’s door.
Considering the conditions that this guy was living in as a prisoner at the hands of serial killers, you can spew whatever you want about his relationship with God, but you have no way of knowing .