The man who launched an arson and homemade explosive attack on a police station in northeastern China earlier this week was a convicted sex offender, local authorities said Saturday.
The Shenyang Public Security Bureau said the 63-year-old man, identified only by his surname, Yang, had bought firecrackers during the Spring Festival and fashioned an explosive device with a trolley bag.
Using a bottle of gasoline as a combustor, he set fire to the traffic police department just after lunch on Thursday, the bureau said in a statement.
The attack killed Yang and injured three others -- two police officers and a member of the public.
Shenyang authorities said in a statement that Yang had previously been jailed for seven years for having sex with a minor.
"He is pessimistic and has a suicidal thought," the statement said.
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"He has been mentally ill and emotionally abnormal in recent times and threatened to commit suicide after killing his wife." Yang had on two occasions this month left suicide notes for his family, the most recent just a day before the incident.
Bomb explosions have occurred elsewhere in China in recent years.
Last July, a 26-year-old man set off a small explosion outside the United States embassy in Beijing, injuring his hand and sending smoke into the air. Police said he was from the northern region of Inner Mongolia, but did not reveal any motive.
In June 2017, a blast outside a kindergarten in the eastern Jiangsu province killed eight and injured dozens. The explosion was blamed on a 22-year-old introvert with health problems who died in the blast.