For more than 40 years, Leslie Waffen was a guardian of national treasures. But for the final 10 years of his career at the National Archives, he secretly peddled some of those rare pieces of history on eBay.

On Thursday, in a federal courtroom in Greenbelt, the 67-year-old Rockville resident was sentenced to 18 months in prison and two years of supervised release for embezzling U.S. property.

Fighting back tears, Waffen told the court that his “passion” for historical audio had become an “obsession.”

It all began, he said, when he started taking recordings home without permission to listen to and determine whether the material was suitable for the Archives’ collection. But he never returned the items.

“I should have returned it. I did not return it,” he said in court, reading from a prepared statement. Over time, his behavior became “compulsive” and “arrogant” as he stole items from the Archives’ permanent collection “with the intent of selling it.”

J. David Goldin, an enthusiast of historic radio recordings who had donated a Babe Ruth hunting recording, helped authorities crack the case. (Jennifer S. Altman/FOR THE WASHINGTON POST)

When Waffen plead guilty in October to theft of U.S. government property, he admitted that he stole 955 items from the Archives, including original recordings of the 1948 World Series and a rare recording of the 1937 Hindenburg disaster. A government expert valued the 955 items at $83,238.

The courtroom was full of relatives and friends. Also present were National Archives staff members and the man who helped authorities crack the case, J. David Goldin, an enthusiast of historic radio recordings who had donated a Babe Ruth hunting recording.

Goldin did not speak during the hearing, but afterward he said he had come to know Waffen and was “disappointed” with what Waffen had done. “I have great respect for Les. I’ve known him since 1976,” Goldin said. “He’s one of the best archivists for sound in the U.S.”

U.S. District Judge Peter J. Messitte said he had received letters from Waffen’s friends, family and neighbors praising his good character and asking the court to take that into consideration during sentencing.

“One hopes as you go forward, you will abandon that parallel universe of crime,” Messitte said.

Messitte said that Waffen’s actions involved not just a monetary issue, but also an issue of trust. Waffen, the judge said, jeopardized the reputation of not only himself, but also of the Archives and other federal agencies.

“You take our history if you take the thing to sustain our history,” Messitte said, echoing the sentiments of Shylock in Shakespeare’s “Merchant of Venice.” A restitution hearing is set for Aug. 13.