What if the Vegas shooter knew his brother was being investigated

What if the shooter some how knew his brother was being investigated by the FBI for CP. If this was an on-going investigation they could've questioned Stephen about his brother's habits before the shooting was ever contemplated. In retaliation for the FBI narrowing down on his brother and maybe even himself, he murdered 58 people. Motive?

Also something to note, an email address of his had the word Powerpuff girls in it and an old picture of Stephen and his brother had a Powerpuff picture reflecting off the wall behind them. Very peculiar.