That's a mistake for the prosecution to contend with in correctly making their case before the court, but it doesn't stop everyone else from casting their own judgement.
I can't think of any other plausible explanation of why he was arrested with $500 in his hand at a specific place that had been prearranged over email, phone calls and texts, other than to commit the rape of a 12-year-old girl, for that price, that had been discussed with the undercover officers - can you?
I’d be curious to hear the Duncan Donuts recording. I think that would be the deciding factor for me.
For all we know it was anime and the cop said it was child porn because he had never seen anime in his life.
Maybe he had an ex that wanted to make life hell for him. Create a new e-mail account using the guys name, use that to create a Craigslist account, do the whole bit. Come back "to pick something up", plant some child porn on his computer; or maybe the "child porn" on the computer wasn't really that childish (either just normal porn, or maybe porn alleging to be 17-year-olds or something). Arrange with the "uncle" (whom you know are the cops) to meet at a place you know he frequents regularly: maybe he just carries $500 with him as a habit; maybe he always stops at the Dunkin Donuts after visiting the payday check casher -- an ex would know that kind of thing. Or maybe come up with some other excuse to get him there with the requisite cash. Or, play then Craigslist game the other way, and arrange for him to be there with the cash -- maybe he thought he was buying a used car, or maybe he actually thought he was buying a used instrument from Craigslist, being sold by a 12-year-old girl!
There absolutely are vindictive people like that in the world; and my guess is there are a lot more vindictive people like that than complete idiots who would ask a complete stranger on Craigslist, out of the blue, to arrange sex with someone under 11. (And then come on Hacker News decades years later to protest his innocence?) "I was framed" certainly seems implausible, but slightly less implausible than the accusation.
EDIT: From the link above:
> Wistocki observed a vehicle approach the parking lot, and an individual exited the vehicle. The individual walked over to Detective Anthony Cimilluca (who was portraying Kelsey's uncle Greco). The individual introduced himself as Joshua Smith, and Cimilluca introduced himself as Greco. Inside the Dunkin' Donuts, Smith gave Cimilluca $500 and asked to meet Kelsey. Cimilluca told Smith that she was waiting outside in a van. The pair exited Dunkin' Donuts and Smith was arrested. Upon his arrest, Smith was identified as the defendant.
Somewhat harder to explain why you introduced yourself as "Smith", and gave $500 to a guy you thought was named "Greco".