So the murder suspect turned out to be a 23-year-old guy called Zachary Capers. He has no connection to the victims that anybody has been able to found. Why he cut a peaceful old couple into ribbons is a mystery right now. The only connection is that Capers was homeless and the murdered lady did some charitable work with the homeless. He might have seen her there and singled her out for some reason.
He was charged so fast because he was picked up on an outstanding warrant shortly to the murders and was acting erratically, leading the police to look at his connection to the murders.