Oh, please... we've read countless stories in which the acts of even the most violent among us are met with complete surprise by friends and family who "never had any idea" such acts would happen. People deal with personal demons all the time, out of sight of those who believe they know them.
OK, so to take your point and extend it...
If Gentle Ben was good at hiding his inner rage then, what’s to say he isn’t doing that now?
Hmmm?