There was no actual reference to it, just that he has been behaving strangely since the fire. I suppose Carl has to be found guilty eventually and this would be an easy way out for scriptwriters.
According to Soap Box on This Morning....He knows something, but nobody know what he knows and if he does know something, nobody knows what it is. It Is something to do with the fire but nobody knows.
In other words, the storyline is not being leaked.