When he testified at his plea hearing, under oath, that he committed the crimes to which he was pleading guilty, he undermined the chance that he could later point the finger at his co-defendant for the crimes he was confessing to have committed. Further, waiting sixteen years before raising the issue doesn't leave much chance that a court will be interested in his regrets over his plea deal. Also, you don't get to pick and choose which parts of a plea bargain you challenge - if he were to have his plea bargain set aside, it would be the whole deal, and he could be prosecuted and sentenced on the basis of all original charges.

I'm not sure what you mean by "one of these forms". Trying to set aside a conviction typically involves extensive research and briefing. There's simply not a form that you can fill out for every need and occasion.

How did you meet this guy? I should mention that there are a lot of prisoners serving long terms who insinuate their way into lives of people on the outside, with claims of wrongful conviction or injustice, in order to get attention, sympathy, and in some cases gifts.