NEW YORK (Reuters) - A grand jury indicted a New York man and his girlfriend following their arrest on Saturday after police found an explosive compound, bomb-making manuals and weapons in their Greenwich Village apartment.

Aaron Greene, 31, appeared briefly in a New York courtroom on Friday, and was informed of the indictment by a judge. He was returned to jail without bail.

Formal charges against Greene were set to be announced at a January 29 court appearance, when he is expected to enter a plea, prosecutors said.

Greene's girlfriend, Morgan Gliedman, who was nine months pregnant when she was arrested, gave birth over the weekend to a baby girl and remained hospitalized in police custody, a law enforcement source said.

The grand jury also indicted Gliedman, according to a law enforcement source. It was unclear when she would be formally arraigned.

Police received a tip about the weapons and potential explosives from someone who had been in the couple's apartment, a police official said. Gliedman was wanted on suspicion of credit card theft, the official said.

Authorities, executing a search warrant of the couple's apartment, found bomb-making instructions, including a manual called "The Terrorist Encyclopedia", high-capacity rifle magazines, a flare launcher, two shotguns, and a plastic bottle containing seven grams of hexamethylene triperoxide diamine, or HMTD, court documents said.

The discovery of the HMTD, commonly used in homemade bombs, prompted an evacuation of nearby buildings, a law enforcement source said.

Interest in the case has been driven by the couple's privileged background. Gliedman's father, Paul Gliedman, is director of radiation oncology at Beth Israel Hospital in Brooklyn, according to a second law enforcement source.

Gliedman studied creative writing at The School of The Art Institute of Chicago, according to her Facebook page.

Greene's lawyer declined to comment on Friday, as did Greene's parents, who were in court for their son's appearance.

(Reporting by Chris Francescani; Editing by Daniel Trotta, Leslie Gevirtz and Richard Chang)