Laurence Duggin was an on-again, off-again, high level Soviet operative in the U.S. State Department from 1933 to 1947.  Duggin was head of the State Dept. Latin America desk.  Even though information on the countries within Duggin’s purview was of only minimal interest to the NKVD, he was still able to acquire documents regarding Europe and most importantly Germany and Japan.

Duggin was first approached by Hedda Gumperz, an exiled German and a Soviet agent living in Washington.  Although Duggin would prove to be one of the Bolsheviks' most useful spies during this time, Gumperz cultivated a relationship with Duggin to get to know his friend Noel Field, who headed the European division.

It is interesting to note that Duggin worked for the Soviets strictly for ideological reasons, and was horrified by the rumors he heard of purges. In fact, in response to a cable sent by Moscow, his handler and New York station chief Boris Bazarov replied:

You ask whether it is timely to switch him to payment?  Almost definitely he will reject money and probably consider the money proposal an insult.  Some months ago Borodin wanted to give Duggin a present on his birthday.  He purchased a beautiful crocodile toiletries case with Duggan’s monograms engraved.  The later categorically refused to take this present; stating that he was working for our common ideas, and making it understood that he was not helping us for any material interest. (p.12)
Later Duggin would try to break away from the Communist underground.  He quit his job at he State Department after he was named by Whitaker Chambers as a Soviet agent, and ran the Institute of International Education.  He then rejected further Soviet attempts to get him to return to spying in his civilian job.

On December 11, 1948 he was questioned by the FBI about Chambers' allegations.  Then on December 20 he either fell from his office window or was pushed to his death.

Source:  The Haunted Wood: Soviet Espionage in America – The Stalin Era
By, Allen Weinstein and Alexander Vassiliev