A retired Army Reserve lieutenant colonel faces up to 20 years in prison and a $500,000 fine when he is sentenced this summer for sharing military secrets with his younger Chinese girlfriend.

Benjamin Pierce Bishop, 60, of Kapolei pleaded guilty Thursday in federal court to one count of communicating national defense information to a person not entitled to receive it and one count of willful retention of national defense information.

Wearing a white jumpsuit and chains, Bishop appeared relaxed as he told U.S. Magistrate Judge Kevin Chang that he sent an email to his girlfriend about a classified conference between the U.S. and South Korea.

"I spoke too much because I said something that was admitted at the conference," he said.

He also admitted bringing classified documents to his home, an unauthorized location for the storage of classified information.

"They should have stayed back at work," he said.

His attorney, Birney Bervar, said the case was not about espionage, but about love. He said the woman was a Chinese national and graduate student at a U.S. university studying the same subject area as Bishop’s expertise. Bishop was trying to help her with her thesis, Bervar said.

"He took some documents home in order to educate himself to help her," he told reporters outside the courthouse. "He did not give her any documents. He did not show her any classified information."

Bervar said the government has no evidence that the woman was a spy or had any ties to the Chinese government for espionage.

Assistant U.S. Attorney Ken Sorenson, who prosecuted the case, said the release of the documents could have been damaging because they set forth defense strategies for the entire Pacific region.

A girlfriend-boyfriend relationship doesn’t mean that the disclosure wasn’t damaging, he said after the proceeding.

"And it doesn’t mean she may or may not have been affiliated with someone else. Once it’s disclosed to another person, we don’t have control over it."

Bishop was a civilian contractor with a top-secret contract with U.S. Pacific Command and a lieutenant colonel in the Army Reserve who routinely had access to classified information relating to cyberdefense operations and strategic operational activities, a court affidavit said. He retired from the Army last year.

The FBI said Bishop met the woman at a military defense conference in Hawaii and began a romantic relationship in June 2011 while he was still married.

In May 2012, Bishop sent information about joint training sessions between the U.S. and South Korea in an email to a person, according to court documents. Bervar identified the person as the girlfriend.

In a search of his home in November 2012, federal agents found 10 documents classified as secret, including the U.S. armed forces’ defense planning guide for 2014 to 2018; information on U.S. force posture in the Asia-Pacific; a summary sheet on the MQ-9 Reaper drone; and the U.S. Department of Defense’s China strategy, court documents said.

Bishop was arrested in March 2013. In June, U.S. District Judge Leslie Kobayashi allowed him to move to a halfway house, but another judge ordered him back to jail in December after he violated the terms of his release by emailing his girlfriend and writing her a letter. Bishop is not allowed to communicate with the woman.

Bishop faces a maximum of 10 years in prison and a $250,000 fine for each count when Kobayashi sentences him June 26. Bervar said the sentencing guideline is two to nine years for each count.

Bishop on Thursday was sent back to solitary confinement at the federal detention center.