his sister-in-law Ruth Greenglass to his NKVD superiors for the use of her apartment as a safe house for photography, the NKVD realized that David was working on the Manhattan Project. He was then recruited into Soviet espionage by Ruth at Rosenberg's behest in November 1944. Greenglass began to pass nuclear secrets to the USSR via the courier Harry Gold, and more directly with a Soviet official in New York City. According to the Venona project intercepts decrypted by the National Security Agency between 1944 and some time in the 1970s, Greenglass and his wife Ruth were given code names. David was codenamed "KALIBR" (Cyrillic: Калибр, "calibre") and Ruth "OSA" (Cyrillic: оса, "wasp"). Greenglass turned down requests from the Los Alamos Laboratory (and Rosenberg) to work on the Operation Crossroads nuclear tests at Bikini Atoll because he wanted to be with Ruth. He was honorably discharged from the Army on February 29, 1946. Greenglass returned to Manhattan, where, with his brother Bernie, and Julius Rosenberg, he ran a small machine shop known as G & R Engineering. On February 14, 1950, Ruth, who was pregnant with their second child, came too close to the gas heater in their Lower East Side apartment, and her nightgown caught on fire. Greenglass extinguished the blaze, but she suffered severe burns. She was taken to Gouverneur Hospital for skin grafts. He suffered second degree burns to his right hand. He was already aware that the UK and US intelligence agencies had discovered that a Los Alamos theoretical physicist, Klaus Fuchs, had spied for the USSR during the war. Through Fuchs' confession, they found that one of his American contacts had been a man named Harry Gold from Brooklyn, New York. Gold had passed Fuchs' information on to a Soviet agent, performing the role of courier, and Anatoli Yakovlev would then pass the information on to his controllers in the USSR. Through Gold, the FBI's trail led to Greenglass and the Rosenbergs, who had allegedly also used Gold as a courier. When Fuchs was first captured, Julius allegedly gave the Greenglasses $5,000 to finance an escape to Mexico. Instead, they went to the Catskills and used the money to seek legal advice. Trial and aftermath David Greenglass was arrested by the FBI for espionage in June 1950 and quickly implicated Julius Rosenberg. He explicitly denied his sister Ethel's involvement when he testified before a grand