Asked about the grenade, the Korean airport security official pointed out that South Korean guidelines list as legal non-flammable, inert cartridges or tins that produce smoke, but said he would have to see the specific item before he could say more.
Customs officers also believed that the lead-filled, leather-coated billy clubs and collapsible baton might be prohibited by California law, according to an affidavit filed in U.S. District Court.
Harris has been charged with one count of transporting hazardous materials, an offense that carries a maximum penalty of five years in prison. He made a brief court appearance Tuesday but his arraignment was delayed until Friday and he was ordered held until then.
Harris is a U.S. citizen whose permanent residence is in Boston, though he recently started living and working in Japan, officials said.
Attempts to reach Harris' family in Boston were unsuccessful. His attorney, Steven Seiden, was unavailable, said spokesman Chris Williams, who described Harris as very intelligent, earning A's in high school and college calculus.
Williams objected to characterizations that Harris was not cooperating with authorities, saying he followed his attorney's advice to exercise his constitutional right to remain silent.
"He has that right. He is an American citizen," Williams said Wednesday.
Harris graduated from Boston University's Metropolitan College in January 2011 with a bachelor of science in biomedical laboratory and clinical sciences, said Constance Phillips, the program director. She called Harris a shy, good student who completed several internships performing research at well-known labs in the Boston area.
Harris traveled from Kansai, in western Japan, to Incheon before landing in Los Angeles. South Korean officials said he traveled on all Asiana Airlines flights, though the airline declined to confirm that, citing South Korean law banning disclosure of passengers' information without their consent.
Security at Japanese airports is similar to security in the U.S. Metal detectors and X-rays screen every person and every bag, both checked and carry-on. Airport and immigration officials at Kansai International Airport said Wednesday that airlines are primarily responsible for luggage inspection, but no problematic cases have been reported recently.
An immigration officer at Kansai, Masahiro Nakamoto, said authorities did not report anything suspicious at the time Harris boarded, but arriving passengers are checked more closely than those leaving the country. Spokesman Keisuke Hamatani said Kansai security officials had not reported any suitcases containing the hazardous materials U.S. authorities say they found in Harris' luggage.
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 into the cabin rather than checked.
"The case does not seem to pose any immediate concerns about aviation security measures in Japan," he said.
Airport police said they do not believe the case constitutes illegal conduct under the Japanese domestic criminal code, but Japan may cooperate at the request of U.S. investigators.
Sullivan reported from Washington. Contributing to this report were Associated Press writers Shaya Tayefe Mohajer in Los Angeles, Elliot Spagat in San Diego, Rodrique Ngowi in Boston, Erika Niedowski in Providence, R.I., Eric Talmadge and Mari Yamaguchi in Tokyo, Alicia A. Caldwell in Washington, and Hyung-jin Kim in Seoul.