Chinese authorities reportedly killed or jailed more than a dozen of the Central Intelligence Agency’s sources in the country from 2010 to 2012, one of the worst breaches seen in the U.S. intelligence community in decades. Ten current and former U.S. officials cited by The New York Times on Saturday spoke on the condition of anonymity about the previously undisclosed spy saga. They said between 18 and 20 CIA assets were killed or jailed on Chinese territory from the end of 2010 to 2012—and the source of the breach is still unknown. At least 12 of the assets were killed, according to the report. Three of the officials interviewed said one of those killed was executed in front of his colleagues in the courtyard of a government building, an apparent message to other CIA assets working in the country. Others were thrown in jail. Officials described the intelligence breach as being on par with American losses in the Soviet Union and Russia after breaches by Aldrich Ames and Robert Hanssen, who betrayed the CIA and FBI in their time. The CIA and the FBI opened a joint investigation into the deaths and disappearances of U.S. intelligence operatives, but they have yet to publicly comment on the matter, according to the report. Although investigators reportedly had a list of suspects, including a Chinese-American who left the agency just before the killings began, no charges were filed and the episode is still a matter of debate within the intelligence community.