Procurators examined the surveillance footage, interviewed witnesses, collected statements and more than 100 pieces of evidence, said Sun Chengyi, head of the Harbin railway transport procuratorate under the Heilongjiang Provincial People's Procuratorate.

"Officer Li's use of the gun conformed with the regulations and law," Sun said.

This conclusion has been further supported by law experts who watched the footage of the incident.

Li possessed a firearms license and had the duty to safeguard the security of the railway station. He gave oral warnings and used his riot stick before shooting. If he had not opened fire, Xu's violence would have posed a threat to public safety, said professor Yang Zongke with Northwest University of Politics and Law.

A police officer on duty must act with dignity because he represents the authority of the law, said professor Wang Lei with Peking University School of Law.

"If he had not opened fire, he could have been accused of dereliction of duty," Wang said.

THE DRUNKEN XU CHUNHE

Xu's mother, Quan Yushun, told police that he had drunk a glass of liquor and half bottle of beer at lunch. The autopsy confirmed that Xu's blood alcohol level was 1.28, much higher than 0.8, which is classed as "intoxicated".

When asked by the police why Xu blocked the security check passage, Quan said: "There was no reason. Just because he had drunk alcohol and he was not in a good mood."

Xu had three children. His wife was mentally ill.

Quan and her three grandchildren had to resort to begging as Xu was "too lazy" to work, said officials and residents of Fengman Village, Xu's home village.

He liked to drink and often asked for help from his mother once he had spent all his money, they said.

The Harbin railway police gave Xu's family 200,000 yuan after his death.

The money had been saved in a bank account in Quan's name. Quan promised to use the money to support her grandchildren, Wang Shuhua, Fengman Village head said.