"The majority of them had some problem with their early education that created a certain vulnerability in their minds," she said.

Li studied philosophy in the early 1980s but was more interested in crimes committed by young people when she graduated from university. The phenomenon was a growing problem at the time.

Yao Jiaxin.[File photo]

"Under the family planning policy that allows most families to have one child, many parents pinned all of their hopes on that sole child," she said. "They turned arbitrary toward their children to force them to realize their dreams but neglected the most important thing - to give love and care to their children."

On Nov 27, 2009, suspect Li Lei allegedly killed six family members in Daxing, Beijing, including his 2-year-old son before running away.

Li was arrested on Nov 28 and told police he killed his family because his parents were "too tough" and his wife "too domineering".

"Based on Li's words, I guessed Li had been spoiled by someone other than his parents when he was a child and returned to live with his parents after he went through puberty," Li said. "Otherwise, a child would not feel his parents had been too tough."

Media reports said Li Lei lived with his grandparents until he was 10 and returned to his parents when his grandparents could no longer control him.

Criminal psychology is widely used to crack criminal cases by narrowing the field of suspects but psychological evaluation is not used as evidence in court.

Li said her insights help her understand that there are usually victims other than the main one in criminal cases.

"I feel bad for the victims but I also feel sorry for the killers because they ruin their own lives to let out their pain," she said.