His attire attracted the attention of law enforcement, and when his luggage was checked the weapons cache was found, authorities said.
The search of his checked luggage uncovered numerous suspicious items, including a hatchet, knives, collapsible baton, biohazard suit, billy clubs, handcuffs, leg irons and a device to repel dogs, authorities said.
The items "looked like a kidnap kit," prosecutor Mills said.
Seiden, who also represents the man believed to be behind an anti-Muslim film that roiled the Middle East, said the clothing worn by Harris when he was arrested is common in Asian countries and described the outfit as resembling martial arts attire.
He disputed the government's contention that body bags were found inside his client's luggage. Harris had a large duffel bag for moving items, the lawyer said.
Harris is a U.S. citizen whose permanent residence is in Boston and was traveling there because his stepfather recently died, Seiden said.
His flight originated in Japan and he got off in South Korea, where security officials screened Harris and his carry-on luggage. The smoke grenade made it onto the plane in his checked luggage, authorities said.
The grenade was X-rayed in Los Angeles and police determined the device fell into a category that is prohibited on passenger aircraft. The knives and items are permissible in checked bags, while the vest and pants are not listed among items prohibited in aircraft cabins.