Harris drew suspicion when U.S. Customs and Border Protection officers at the airport noticed he was wearing the bulletproof vest and fire-resistant pants under his trench coat. That triggered a formal investigation by Homeland Security special agents.
A search of Harris' checked luggage uncovered numerous suspicious items, including knives, body bags, a hatchet, a collapsible baton, a biohazard suit, a full-face respirator, billy clubs, handcuffs, leg irons and a device to repel dogs, authorities said.
The smoke grenade was subsequently X-rayed by the Los Angeles police'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 airplane with smoke or cause a fire," federal officials said in a news release.
Many of the other items in Harris' luggage — including the hatchet and knives — wouldn't violate 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 U.S. District Court.
A Customs and Border Protection official said Tuesday night that Harris was not enrolled in any of the U.S. government's trusted traveler programs, which could have allowed faster processing through security or customs. The official spoke on the condition of anonymity because he was not authorized to discuss details of the ongoing investigation.
Harris traveled from Kansai, Japan, to Incheon, Korea, before landing in Los Angeles.
Yasunori Oshima, an official at Japan's Land and Transport Ministry's aviation safety department, said there had been no official inquiry or request from U.S. authorities to look into the case, which he said would have been more of a concern if the hazardous materials were brought on board rather than checked.