The problem with your hypothetical is that it doesn’t exist. The information is coming from an axe murderer and your just magically asserting the family is real and what he says is real.
The problem is when your an axe murderer, I no longer trust you. Just as we shouldn’t trust the USA because they do all the bad things they say others are doing. It’s an accountability issue. Which is if you want to say your a good guy, you kind of have to actually be a good guy.
*Edit. This is why I said innocents get caught up in gang wars but the police can’t do anything because the source of information is gangsters