Prosecutors in the western Japanese prefecture of Nara plan to indict the suspect in the shooting death of former Prime Minister Abe Shinzo on Friday.
Police arrested Yamagami Tetsuya after Abe was shot dead on July 8 last year while making a campaign speech in Nara.
He is being held on suspicion of murder and illegally manufacturing and using firearms.
The 42-year-old told police he was motivated by a grudge against a religious group widely known as the Unification Church. He claimed his mother's huge donations to the group left his family in financial ruin.
He said he targeted Abe because he believed the former prime minister had close ties with the group.
The prosecutors have determined that Yamagami is mentally fit to stand trial. They based their assessment on a psychiatric evaluation that lasted nearly six months.
Investigative sources quote Yamagami as saying during the evaluation that he wanted others to hear more about the group and his family environment.
The case will be heard in a lay judge trial. Observers say they expect the trial to disclose the details and motive behind the incident that has had an immense impact to Japanese society.