Without pictures, "head smashed in" doesn't really mean anything. What was actually posted is, "looked as if half of his head had caved in". In some mind's eyes, that shows up as a smashed head, while others may interpret it it as some type of indentation. The "goo" coming out of the head could have been saliva/goo coming from its mouth for all we know.
I didn't say the proposed theory is wrong, just that it's only a theory and shouldn't be stated as fact when so little definitive information has been given. Suggest the guy ask around or something, but don't tell him that you KNOW someone did this when there isn't any concrete evidence to show that.