WASHINGTON — (CNN) A Navy officer has been charged with espionage and attempted espionage, among other accusations, in a proceeding that has been designated a national security case.

Three U.S. defense officials named the Navy officer as Lt. Cmdr. Edward Lin. Multiple attempts by CNN to reach Lin, his family, or his attorney have been unsuccessful.

Lin was arrested about eight months ago, but information about his case didn’t become available until after a preliminary hearing Friday.

Key parts of the charging sheet are still redacted.

A defense official told CNN Monday that investigators are still trying to determine who Lin was spying for, though China and Taiwan are possibilities.

The full scope and breadth of the information provided is unclear, the official said, but the suspicions stem from the work he was doing at the time of his arrest.

The official said investigators found enough evidence to be able to bring charges, but much more is needed to determine exactly what information was passed and to whom.

According to his military record, Lin enlisted in 1999 and was commissioned in 2002, serving as a naval flight officer.

At one point he worked on the staff of the assistant secretary of the Navy for financial management and comptroller in Washington.

He received two commendation medals and various other service and achievement medals.

Friday’s Article 32 hearing was a preliminary hearing, to be followed by a decision on whether the charges are referred to a court-martial.

LIn was taken into custody at an airport in the U.S. Pacific Command region while heading to a foreign country, a U.S. official with knowledge of the investigation told CNN.

Since his arrest, Lin has been in pretrial confinement and is now being held in a brig in Chesapeake, Virginia, the U.S. official said.

The charging sheet shows he was assigned to Commander Patrol and Reconnaissance Group.

The unit is based in Norfolk, Virginia.

Both the Naval Criminal Investigative Service and the FBI continue to investigate the case, the U.S. official said.

The most serious charges against Lin are two counts of espionage and three counts of attempted espionage.

The other charges include violations related to wrongly transporting material classified as secret and failing to report the compromised information.

Lin is charged with three counts of “false official statement” for failing to report foreign travel and putting false information on documents.

There is one count of paying for a prostitute and another for adultery.