(NewsNation) — Mourners gathered in Nara, Japan, on Saturday, some shedding tears, to bemoan the assassination of former Japanese Primer Minister Shinzo Abe.

The suspect in Abe’s killing is believed to have used a homemade gun to murder the ex-leader while he was giving a speech in Nara on Friday.

On Saturday, flags in Washington, D.C., remained at half-staff, while in Japan, an investigation into possible security failures around Abe’s death was underway.

The police chief of Nara acknowledged to local reporters that there were flaws in the security plan around Abe before he was assassinated by a suspect who is believed to be a former member of the Japanese Navy.

Tetsuya Yamagami, 41, was arrested at the scene by police and has since been charged with murder.

A woman who lived below Yamagami in an apartment complex told Reuters he seemed to be a “loner” who was “bothered by something.”

Police say Yamagami held a grudge against Abe due to his alleged ties to a religious organization to which Yamagami’s mother also belonged to. 

Japanese media reported Yamagami hated the religious group, but did not identify the organization. 

Abe’s assassination, meanwhile, was at the forefront of conversations at the G-20 summit in Bali.

“The alliance between Japan and the United States has been a cornerstone of our foreign policy for decades,” said U.S. Secretary of State Anthony Blinken. “Prime Minister Abe really brought that partnership to new heights. The friendship between Japanese and American people is likewise unshakeable.”