I was watching this movie last night and I noticed something. When Alex arrives at Frank Alexander’s house for refuge, all bloody and beaten up, Alex clearly remembers Frank and is a bit scared that Frank will remember him. But, at first, Frank only remembers Alex from the papers as the boy who underwent the governmental treatments. Why wouldn’t he realize that Treatment-Alex was the same boy who helped rape his wife and beat him up? He only remembers that it’s Alex when Alex is singing “Singing in the Rain” in the bathtub and it sparks his memory. Surely they must have written that in the articles or made that information public, because earlier Joe, the guy who rented Alex’s old room, says he heard from Alex’s parents everything Alex did.
Good Question;
Here’s some answers from a while back
http://boards.straightdope.com/sdmb/showthread.php?threadid=50672
hope it does the trick 
They probly never found out that Alex raped his wife.
"I love the movie West Side Story, but there is a mistake in it, a big old glaring mistake. You know what it’s about, right? There’s this guy Tony, he’s a white man, he’s wonderbread white, he’s a white white white white guy. White white Tony, ok? So he runs into this completely Latino, Puerto Rican neighbourhood, and he yells MARIAAAAAAAAAAAAAAAAAA!
"And only one woman comes to the window!
“You yell Maria like that in my Italian neighbourhood, you get twenty fat women in aprons. 'Whaddaya want? ‘Smatter?’”
-Lea DeLaria
I’m reasonably certain that Alex didn’t talk to his parents at the breakfast table about last night’s robbing and raping. When Joe said that Alex’s folks told him “everything”, it was presumably everything they knew, which wasn’t quite everything.
Coincidentally, I just watched this movie for the first time Friday night, and I was singing “Singing in the Rain” on the drive to work today…