"He may have interests that are not of the norm, but that doesn't mean he's carrying out any type of harm to anyone," Seiden said.
The bespectacled Harris was shackled in handcuffs and wore a white prison-issued jumpsuit, along with a blue surgical mask over his mouth due to a throat infection.
Before the hearing, he crossed and rubbed his arms, appearing to be cold. He often turned and spoke with Seiden.
Harris is a U.S. citizen whose permanent residence is in Boston, though he recently started living and working in Japan, officials said. Harris was returning to Boston because his stepfather had recently passed away, Seiden said.
He got off his flight in South Korea before he headed to Los Angeles. South Korean security officials screened Harris and his carry-on luggage, but the smoke grenade made it onto the plane in his checked luggage, according to a U.S. Homeland Security official briefed on the investigation.
The official was not authorized to discuss the case publicly and spoke on condition of anonymity.
The smoke grenade was X-rayed by police bomb squad officers in Los Angeles, who said the device fell into a category that is prohibited on board passenger aircraft. It is banned from planes under the United Nations' explosives shipping rules.
Most of the items wouldn't violate Transportation Security Administration guidelines for what is permissible in checked luggage, and the protective vest and pants are not listed among items prohibited on flights.