NHK has learned that police officers on duty at the venue where former prime minister Abe Shinzo was giving an election campaign speech didn't recognize a suspicious man in the crowd until hearing the first gunshot.

Abe was fatally shot from behind on Friday afternoon during an appearance in the western city of Nara.

Police arrested the gunman, Yamagami Tetsuya, on the spot. He is an unemployed resident of the city.

Investigators have been questioning the 41-year-old on suspicion of killing the former prime minister.

Yamagami allegedly approached Abe by walking diagonally from behind, and firing two shots at a range of several meters.

The National Police Agency says that considering the circumstances of the crime scene, it plans to review the day's security arrangements for the former prime minister.

The agency cites possible problems with police arrangements for patrolling the area behind where Abe was speaking.

Some security experts point out the seriousness of police officers failing to stop the gunman from firing at Abe.

They say, first and foremost, the officers should have prevented the assailant from getting anywhere near Abe.