The alleged assassin who shot and killed Shinzo Abe on Friday believed that the former Japanese prime minister was a member of a "specific organization," according to authorities.

Tetsuya Yamagami, 41, was taken down moments after allegedly opening fire on the 67-year-old former leader during a campaign address in the western district of Nara.

Yamagami allegedly revealed to detectives that he plotted to kill Abe because he believed the ex-prime minister was affiliated with a group he had a grudge against.

The police withheld the organization's name and beliefs, and it was unclear whether the group existed.

According to authorities, the alleged assassin's resentment did not appear to be political.

During his interview, Yamagami was composed, and detectives are still attempting to determine whether he acted alone, police said.

The alleged murderer was a Nara resident who worked for Japan's Maritime Self-Defense Forces for three years but now appears to be unemployed, according to the police.

Yamagami stood behind Abe minutes before he opened fire with a handmade firearm, as evidenced by the surfacing images and video.

Abe, Japan's longest-serving prime minister, had just begun speaking when the first shot rang out. As the second shot was fired, the politician could be seen clutching his chest and slowly falling to the ground.

Guards promptly subdued the assailant, and his double-barrelled, black firearm was nearby.

Abe was pronounced dead five and a half hours after being brought to the hospital and receiving more than one hundred blood transfusions.

According to investigators, he bled to death from severe injuries to his heart and right side of his neck.

Abe's protégé, Japanese Prime Minister Fumio Kishida, stated, "I am simply speechless at the news of his passing."

"This attack is an unforgivable act of brutality that occurred during the elections, the very foundation of our democracy."