Prosecutors on Monday raided the headquarters of the state spy agency as part of their ongoing investigation into allegations that it was involved in fabricating evidence to charge a high-profile North Korean defector with espionage.

   The National Intelligence Service (NIS) is under suspicion of systematically fabricating immigration records that were used in the case of Yoo Woo-seong, a former Seoul city government official charged with handing over to Pyongyang personal information of more than 200 North Korean defectors, and handing them over to the prosecution.

   A team of three prosecutors and some 10 investigators at the Seoul Central District Prosecutors' Office obtained computer hard drives and confidential documents from the NIS headquarters in Naegok-dong, on the southern edge of Seoul, to corroborate the charges, prosecutors said.

   The raid is dealing another blow to the NIS, which is still reeling from allegations that it attempted to sway public opinion ahead of the 2012 presidential election.

   After a local court acquitted Yoo of espionage charges last year, prosecutors appealed the verdict and submitted three Chinese immigration records from the NIS on his visits to the North, which the Chinese Embassy claimed were forged.

   According to the sources on Monday, the prosecution team in charge of the case has learned that Lee In-cheol, an NIS official working as a South Korean consul in China's northeastern city of Shenyang, received a confirmation letter from its key collaborator and handed it over to the prosecution.

   The document, published by local authorities in Helong, a northeastern Chinese city bordering the North, confirms that the Chinese authorities issued the immigration record that states Yoo crossed the border into North Korea twice between May and June of 2006. 

   The spy agency has long claimed that it obtained the document, different from the two others, via a formal diplomatic channel, dismissing chances that any brokers intervened.

   "The fax number printed on the document from Lee was not the one used by the Helong office," a source said. "The prosecution suspects that Lee sent a document forged by an NIS aide."

   So far, the investigators have secured a statement from another key NIS collaborator, identified by his surname Kim, who forged one of the three documents that was published by the Sanhe Immigration Office in China.

   The 61-year-old Kim, meanwhile, has recovered from serious injuries incurred from last week's suicide attempt and been sent to a general ward, according to officials of his hospital.

   As a key aide to the intelligence agency and a witness of the scandal, Kim, a former North Korean defector with Chinese nationality, has been under a prosecution probe. He told the prosecution that he had forged the Sanhe document and handed it to the NIS. (Yonhap)