A man dressed in a bulletproof vest and fire-resistant trousers was arrested at Los Angeles International Airport after a smoke grenade, gas mask, leg irons and weapons were discovered in his luggage, federal authorities said.
Yongda Huang Harris, 28, was arrested on suspicion of transporting hazardous materials on a flight from Japan to Boston, US Immigration and Customs Enforcement officials said.
Harris was not co-operating with federal officials attempting to interview him, according to a US official, who said Harris is not believed to be linked to a terrorist organisation, but his motive has not been determined.
Harris is a US citizen whose permanent residence is in Boston, and he recently started living and working in Japan, officials said. He travelled from Kansai, Japan, to Incheon, South Korea, before landing in Los Angeles.
He has been charged with one count of transporting hazardous materials, an offence that carries a maximum penalty of five years in prison. He made a brief court appearance and his detention hearing was postponed to Friday.
Harris's retained lawyer, Steven Seiden, is unclear what Harris had on his body and what he had in his checked-in baggage. The defence lawyer's spokesman described Harris as "very intelligent", earning As in high school and college calculus. Mr Seiden also represents Mark Basseley Youssef, the man behind the anti-Islam video that recently sparked violence in the Middle East.
Harris drew suspicion on Friday when US Customs and Border Protection officers at the airport noticed he was wearing the bulletproof vest and fire-resistant trousers under his trenchcoat. That triggered a formal investigation by Homeland Security special agents.
In a search of Harris's checked luggage, numerous suspicious items were uncovered, including knives, body bags, a hatchet, a collapsible baton, a biohazard suit, a full-face respirator, clubs, a respirator, handcuffs, leg irons and a device to repel dogs, authorities said.
The smoke grenade was subsequently X-rayed by the Los Angeles Police Department's bomb squad. Officers said the device fell into a category that is prohibited on board passenger aircraft by the United Nations. "Depending on the conditions when it is ignited, the smoke grenade, made by Commando Manufacturers, could potentially fill the cabin of a commercial plane with smoke or cause a fire," federal officials said in a news release.
Many of the other items in Harris's luggage - including the hatchet and knives - would not violate posted Transportation Security Administration guidelines for what is permissible in checked luggage. However, customs officers Kenny Frick and Brandon Parker believed in their initial investigation that the lead-filled, leather-coated billy clubs and a collapsible baton may be prohibited by California law, according to an affidavit filed in US District Court.