XUZHOU, China (Reuters) - The man who set off a self-made explosive device outside a Chinese kindergarten killing eight people and injuring 65 others on Thursday had a neurological disorder and had scrawled words for death on the walls of his home, officials said on Friday.

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The 22-year-old man, surnamed Xu, was among those killed in the blast near the entrance to the kindergarten in Xuzhou, a city in the coastal province of Jiangsu, police said in a briefing shown on state television.

The official Xinhua news agency said police were considering the act a “criminal offense”.

Xu had dropped out of an unnamed school due to his neurological condition and rented an apartment near the kindergarten, China Central Television said.

“Self-made explosive device materials were found in his apartment, and on the walls in many places were handwritten words such as kill, death, destroy and terminate,” it said.

Two people died at the scene of the blast and six more died from their injuries in hospital. Xinhua reported on Thursday night that eight people were in a critical condition.

Pictures circulating on Chinese social media showed about a dozen women and children lying on the ground in what appeared to be the immediate aftermath of the blast.

One video showed an injured woman with scorched clothing staggering unsteadily, while others sat on a floor holding crying children in their arms.

Reuters could not independently verify the authenticity of the videos. None of those injured were children or teachers, Xinhua said.

“When I arrived, the scene was messy, both adults and children were lying on the ground. I felt very scared,” a local shopkeeper Wei Xunying, who rushed to the site, told Reuters on Friday.

China’s Ministry of Education issued a statement demanding that education officials strengthen security around schools to ensure the safety of students and teachers.

Local authorities said that contrary to early reports the blast did not occur while parents were picking up children after school, according to the People’s Daily.

Explosives are relatively easy to obtain in China, home to the world’s largest mining and fireworks industries.

Violent crime is rare in China compared with many other countries, but there have been a series of knife and axe attacks in recent years, many targeting children.