But that alone is not perfect. For the actor playing the "hired killer" and accomplices could have lured and goaded the perp on in a conspriracy (a conspriracy of the police) to set up the perp. This does happen. It is NOT clear that the perp would have ever taken matters as far as were taken without the playacting that tempts him to it.
What crime happened here? Ritter went to a Burger King where an ADULT woman waited for him. Did he think she was underage? Well, acting is hard, I say. While the intent of the police was to appear as if they were a "14 year old", there are many nuances even in an on-line chat that could have consicously or sub-consciously clued Ritter in to the idea he was actually engaging with and adult. Furthermore the police are consciously engaged in trapping behaviour and that colors the play-acting conversation as well.
Those are factual objections which is why we have trials. My sense of the decoy is that she must have looked convincingly underage. As to the content of the chat, that could be inspected as well, but again, I suspect that the cops were careful not to be ambiguous or hint at anything other than the mindset of a 14 year old. If the cops did their job well then those defenses wouldn't succeed. And presumably Ritter saw the young girl in the restaurant and continued to proceed with his actions.