Criminal Investigator A. took passer B.

Criminal Investigation Officer A. mistook passer B. for the wanted killer (according to the compiled photograph and verbal description). A., following B., waited for him to enter the entrance of the house and decided to “take” him there. Suddenly, he attacked B. from behind, but he managed to shake A., and rushed up the stairs. A. in the fall hit hard and realized that he couldn’t catch B. Having snatched a service pistol, A. opened fire on B.´s flickering staircase in the opening. Two shots hit the target - B. was seriously wounded. He was detained by a riot police officer.
It turned out that B. was not at all the killer that A. was hunting for, he explained his resistance by the fact that he had no idea that the attacker was a police officer. Forensic medical examination identified B.´s injuries as serious harm to health. Give a criminal assessment of A.