A man was arrested Saturday in Fukui Prefecture for allegedly flying the drone found earlier this week on the roof of Prime Minister Shinzo Abe’s official residence, investigators said.

Yasuo Yamamoto, 40, of the city of Obama, presented himself to the Fukui Prefectural Police on Friday evening and said he landed the drone on the rooftop of the prime minister’s office to protest the government’s nuclear energy policy.

Yamamoto had sand with him and what appeared to be the controller for a drone, sources said. He was quoted as saying he had put sand from Fukushima Prefecture, home to the meltdown-ridden No. 1 nuclear plant, into a plastic bottle that was attached to the unmanned aircraft.

Tokyo police confirmed Friday that the bottle contained sand and were trying to determine whether it came from Fukushima, sources said.

According to the Metropolitan Police Department, Yamamoto said he flew the drone toward the prime minister’s office at 3:30 a.m. on April 9, nearly two weeks before it was discovered Wednesday. Police were speculating that the device had landed more recently.

Yamamoto told investigators he carried out the stunt by himself, and police searched his home in Obama on Saturday. He is being held on charges of forcible obstruction of official business.

Meanwhile, a blog entry apparently posted by Yamamoto on April 12 says he left his hometown on April 7 and arrived in Tokyo’s Akasaka district, near the prime minister’s office and the Diet building, early the following day with the intention of launching the drone.

However, the posting said bad weather forced him to give up that day, so he returned to the area on April 9 and flew the drone out of a parking lot.

The drone, bearing a radiation sticker and carrying a radioactive payload, was found on the roof of the prime minister’s office at about 10:30 a.m. Wednesday. According to the police, the drone was equipped with a camera, what appeared to be two flares, and a brown container of a liquid that later turned out to have a small amount of cesium in it.

Aerial footage of the roof of the prime minister’s office taken on April 15 shows a black object matching the color of the drone.

Fukui Prefecture is the nation’s nuclear heartland, hosting over a dozen nuclear reactors on the Sea of Japan coast. Last week, the Fukui District Court endorsed a citizens’ bid to halt Kansai Electric Power Co.’s effort to restart two idle reactors at the Takahama nuclear plant. The government says it has no plan to push for restarts, but the utility is appealing the injunction, granted on safety grounds.

The drone was also equipped with a global positioning system that provides information about its flight path, sources said. A digital camera on the drone, believed to be a Phantom 2 sold by Chinese manufacturer DJI, was connected to a transmitter that can send recorded footage to a remote monitor. The Phantom is only sold in white, but the one found on the rooftop had been painted black.

On Friday, police and ministry officials held their first meeting at the prime minister’s office on drone regulation and began exploring legislation to regulate flights above sensitive facilities. Plans under consideration include obliging drone buyers to register their name and address.

“We need to immediately establish” legislation on drone usage, Chief Cabinet Secretary Yoshihide Suga said at the meeting, which included officials from the ministries that oversee transportation, internal affairs, and trade and industry.

The government is also expected to weigh the introduction of a licensing system, maintenance rules and mandatory insurance, according to the Land, Infrastructure, Transport and Tourism Ministry.

Suga described the incident as “a grave issue in terms of crisis management.” He said drones “could have a substantial impact on public safety and privacy protection, depending on how they are used.”

Toshihiro Nikai, chairman of the ruling Liberal Democratic Party’s General Council, said Friday that lawmakers need to submit a bill to prohibit drones from being flown above important facilities.

Suga said the previous day that the government will consider legislation to regulate drone flights before the Diet’s summer recess from late June.