Japanese police have confiscated metal tubes, tools and possible gunpowder from the home of a man suspected of throwing what was believed to be a homemade pipe bomb at Prime Minister Fumio Kishida at a campaign event, rekindling worries about the growing threat of easy-to-make weapons in Japan.

Witnesses say they saw an object that looked like a thin metal thermos flying overhead and landing near the prime minister. Kishida was safely evacuated before the device exploded, the crowd fleeing in panic as white smoke surrounded them.

Police have confirmed one injury to a police officer. Experts say a pipe bomb likely caused the explosion, and the impact and amount of smoke suggest it probably wasn’t that powerful.

The 24-year-old suspect, Ryuji Kimura, was wrestled to the ground at the fishing port of Saikazaki in the western Japanese city of Wakayama on Saturday, just before Kishida was to make a campaign speech for a local governing party candidate.

On Monday, police sent Kimura to local prosecutors to extend his detention for 10 days for further investigation. He currently faces an allegation of obstruction of duty, but experts say additional allegations such as assault and attempted murder are possible.

In a raid Saturday night at Kimura’s home in Kawanishi city, more than 100 kilometers (60 miles) northeast of Saikazaki, police confiscated unidentified powder, metal tubes and various tools that were possibly used to make the device thrown at Kishida.

Police said they confiscated two possible metal pipe bombs at the site, one that exploded but largely retained its shape, and another that was in the suspect’s hand at the time of the arrest along with a cigarette lighter. Police also found a fruit knife in his bag.

The crudely constructed weapons and the outdoor election campaign setting were reminiscent of the assassination of former Prime Minister Shinzo Abe nine months ago with a handmade double-barrel gun.

Violent crimes are rare in Japan. With its strict gun control laws, the country has only a handful of gun-related crimes annually, most of them gang related. But in recent years, there has been growing worry about homemade guns and explosives.

“The situation surrounding homemade explosives is becoming a considerably serious problem,” said Nobuo Komiya, a Rissho University professor of criminology. “Not just bombs. Anyone can even make real guns using 3D printers.”

They cannot be regulated because their ingredients are legally available, he said.

The problem is that Japanese protection of dignitaries and public safety are still largely based on defense against knifings. Japanese security guards are well trained for close combat in knife attacks but inexperienced in dealing with bombs and firearms, he said.

“Police must be prepared for crimes in which handmade guns are used,” National Public Safety Commission Chair Koichi Tani said earlier this year. Police have stepped up “cyberpatrols” to detect illegal weapons production and trade, while requesting internet sites to remove “gun production methods and other harmful information.”

Tani has pledged to beef up security ahead of elections in late April and the Group of Seven leaders’ summit in May.

The latest case raises questions about whether any lessons were learned from the assassination of Abe, which prompted police to tighten protective measures after an investigation found holes in his security.

There were no bag checks at the venue, and no bulletproof shield was provided for Kishida. He sampled local seafood as he stood next to residents, then walked to the speech site, where he stood a short distance from the crowd with no physical barrier in between — something unlikely in the United States.

Making public appearances, mingling and shaking hands are important in getting votes in Japanese elections, rather than presenting policies, and politicians tend to get close to the crowds. But experts say there should be several layers of protection for them and other dignitaries.

So far, Kimura has refused to talk to the police, and the motive for the attack is not yet known.

Abe’s alleged assassin, Tetsuya Yamagami, who has been charged with murder and several other crimes including violating gun-control laws, told authorities soon after his arrest that he killed Abe because of the former prime minister’s apparent links to a religious group that Yamagami hated. In statements and in social media postings attributed to him, Yamagami said his mother’s donations to the Unification Church bankrupted his family and ruined his life.

Handmade bombs are not new in Japan, where non-lethal versions of explosives such as Molotov cocktails and pipe bombs were often used by student radicals and extremists in the 1960s and 1970s to throw at riot police and damage property.