Evidence has been found that could help explain the motives of the lone gunman behind one of the worst mass school shootings in American history, police said today.

The massacre of 26 children and adults at an elementary school in the US state of Connecticut elicited horror and soul-searching around the world even as it raised questions about why the gunman, a 20-year-old described as brilliant but remote, would have been driven to such a crime and how he chose his victims, some as young as five.

Some parents who lost children in the Sandy Hook shooting may never recover from the pain of their death, an expert in post-traumatic stress said today.

Police in Connecticut have said the gunman who killed 20 children at a school in America was "remote" and may have suffered from a personality disorder.

The head of the Connecticut primary school devastated by a shooting rampage was among the victims, an official said today.