the man who killed his neighbour terrence freebody 's head , cutting his throat and stabbing him multiple times in the dining room of his home on july 2012 .
forensic psychiatrist professor paul mullen examined costa after the attack and believes there was evidence of the accused 's state of mind declining in the lead-up to the incident and also during the event .
he also said the trail of faeces from the crime scene to the toilet were police found costa suggested his confused mental state .