Any particular reason to want him to face more charges? Consider:
- He's 18 now. He started this when he was 16 or so.
- 4 years is about a quarter of his life-to-date. And he's been in jail for some months already, if you were inclined to quibble.
- He is (apparently) cooperating with authorities to track down those who hired him.
Questions:
- Do you think that throwing him behind bars for 8 years, or 12, or 20, would make him less, or more likely to re-offend? Do you think he would come out of prison with a better or worse outlook?
- Do you think he would continue cooperating with authorities, if you sent him through the courts again after having pleaded?
- Do you think that society would be safer, were he to have a longer sentence?
Failing rehabilitation and safety concerns, what you're left with is vengeance. Putting him in jail for a longer time isn't going to make the people he swatted any less traumatized. (The reports don't say his swatting resulted in deaths, so I don't say "less dead".)
He's already ruined his life. He'll be a convicted felon until he is dead, with all the limitations society puts on them. You want him to stay in jail longer, simply to inflict more pain?