Why? Apparently, they think they are So Important that we need to know that they like this fellow.

It was a character witness letter written to sway the judge's decision.

they should never have done it to begin with

Not if they believed he was guilty. On the other hand they personally don't have any way to know what really happened, and may believe that being 20 years later he is a changed man now. And these are probably bleeding heart liberals who want to abolish the prison system. If they were actually being consistent (not that I'd expect it) they would be soft on crime with their own friend too.

Why? Apparently, they think they are So Important that we need to know that they like this fellow.

It was a character witness letter written to sway the judge's decision.