Police in Wakayama prefecture, western Japan, have seized documents related to a lawsuit filed by a man arrested on suspicion of throwing an explosive toward Prime Minister Kishida Fumio during an election campaign appearance last Saturday. The suspect, Kimura Ryuji, sued the government for not being allowed to run in an Upper House election last year.

Twitter posts apparently by the suspect repeatedly criticized election systems. The suspect sued the government last June, arguing he could not run for office because of the law that stipulates the age requirements for eligibility and the need to pay a deposit to run for office.

It has now come to light that the police confiscated documents related to the lawsuit during a search of the suspect's home.

Investigators say the suspect's mother learned of the lawsuit only when the documents were delivered to their home.

The district court dismissed the case in November last year. Kimura appealed to the Osaka High Court, and the ruling is expected next month.

The police are investigating whether the suspect planned his attack on the prime minister due to his dissatisfaction with the election system as it happened while his case is still in court.