I'm not sure how you interpret this story to represent this comment, but it appears to me that Robert's sister likely invited him to her Bible study, not because he is a Christian but expressly because he is not. He was likely dragged there by his wife Corinna. This seems to be corraborated by the ABC story:
Members of both Woodhull’s and Castillo’s family urged her not to marry him.
“It’s a testament to the kind of person she was that she went through with it, thinking she could help him,” the prosecutor said. “I can’t believe that she knew her wedding vows would ultimately be her death sentence.”
So Corinna, against the advice of everyone who knows Robert, marries into an abusive relationship thinking she can help him, and brings him to his sister's Bible study, where he stabs her in a supposed drug induced rage, and you interpret his actions as an accurate representation of Christian love? Robert doesn't represent even Wordly love in this story, let alone Christ like love.
Ironically, a bolt-action hunting rifle which is legal in all 50 states would be a much better choice for an assassination attempt than "assault rifles" like an AR-15 or the even less accurate AK-47. So not only can they not shoot, they apparently don't know anything about rifles either.