Someone I know has been victimized by a predator in their youth. The things they did were awful. This person was young and felt ashamed and confused and deleted all the evidence. They are now trying to get revenge. Can I try to do a "to catch a predator" type thing and expose them to the police to help the case? I wouldn't initiate anything and let them incriminate themselves and play the long game.
If this is not a hypothetical, forget it.
Police are presumably interested in catching the predator. They would not be helped by amateurs "collecting evidence" and muddling the waters. I hope you are aware that the protocols underlying the internet were not written with forensic analysis in mind. You cannot assume that a message which looks as if it came from a certain person actually came from that person. To get reasonable certainty, someone has to get into the records of the internet service provider or seize the physical device, and vigilantee investigations will accomplish neither.
I'm also deeply worried that this "long game" of yours would involve illegal acts at some point.
- You would build a fake persona. In addition to a name and age, does this persona have a social media presence? Pictures? Selfies? Where do you get them? Using pictures of a real person that way could be illegal, and even if there were loopholes it would be highly immoral to do that to a person.
- That fake persona would then start to exchange messages of slowly increasingly sexual content, unless all you write on that account is "hmm," "wow," and "gosh."