Details matter.
If dad caught the guy in the act with his kid - then case closed.
From there it gets more complicated...
I'm sure many details will come out and it will be high profile. This story is just made for Court TV. Especially with Sherman for the Defense.
You are right, the details are very important in this case. This article leaves too many questions frankly. The only way this would be justifiable to me would be in the situation you mentioned - having actually caught it going on and it being an immediate reaction... It would then be understandable, IMHO.