The spy agency official detained in connection with the evidence-forgery case led the investigation into Yoo Woo-seong, local media reported Thursday, fueling speculations over involvement of ranking National Intelligence Service officials. The news comes as another mid-level NIS official, identified by the surname Kwon, became yet another key suspect in the expanding case.

According to a report citing unnamed sources, the NIS official identified Kim, who was detained on Wednesday, as the one who headed the investigation into Yoo.

Yoo, a former Seoul City official of North Korean-Chinese origin, is accused of spying for Pyongyang. The NIS is alleged to have provided the prosecutors’ office with forged Chinese immigration documents to support its case against Yoo, who was initially acquitted.

“Kim was the chief of the investigation (into Yoo) when the evidence was forged,” an unnamed official was quoted as saying.

It remains unknown whether Kim headed the investigation from the outset or took over at a later point. However, the investigators are said to have sufficient evidence implicating him as the man in charge when the documents in question were obtained.

The investigators now suspect that Kim ordered the immigration records to be obtained, and that he told NIS official Lee In-cheol to fake additional documents to verify the records as authentic.

Kim denies the allegations and has told the prosecutors that the NIS collaborator, also named Kim and now in custody, secured the documents on his own initiative.

As for Kwon, who was questioned on Wednesday, the prosecutors suspect that he was deeply involved in the process. Since February Kwon has been serving as the deputy consul general at the South Korean diplomatic mission in Shenyang, China.

He is also reported to have worked with the team investigating Yoo since August last year. Kwon’s role in the investigation is said to have been collecting information from China.

The main opposition Democratic Party honed in on the latest developments to support its often-repeated claims.

“This tells us that the NIS’ evidence-forgery case was conducted systematically, and feeds the suspicion that (the issue) was reported to the NIS chief Nam Jae-joon,” DP spokesperson Rep. Han Jeoung-ae said.

“It is becoming clear that a special counsel investigation is the only solution. The Saenuri Party should accept the special probe proposed by the DP and collaborate in reforming the NIS.”

By Choi He-suk (cheesuk@heraldcorp.com)