Morgan Gliedman, 27, daughter of a prominent oncologist who gave birth after her arrest, and her boyfriend, Aaron Greene, 31, son of the president of an artwork-restoration business, were charged with criminal possession of a loaded firearm and criminal possession of an explosive substance, The New York Times reported.
Authorities said investigators seized 7 grams of hexamethylene triperoxide diamine, an explosive chemical, at the couple's Greenwich Village apartment.
"This is a serious explosive used in terrorists' attacks previously," city police spokesman Paul J. Browne said. "We have not yet determined why Greene had them in his possession.
"It's an ongoing investigation that aroused our concerns, obviously, because of the weapons, including the explosives, and the material found in the apartment, including these handbooks involving weapons of mass killing. What it means is still unknown.
"We haven't made a connection to any known plot or any connection to any known terrorists."
Greene did not appear to be active in any political movements, police told the newspaper.
Police also found two shotguns -- one with the barrel sawed off -- dozens of shells, a flare launcher with four flares and nine high-capacity rifle magazines, authorities said.
Browne called the couple "admitted heroin addicts."