Won Sei-hoon, the former head of the National Intelligence Service (NIS), is suspected of ordering an online smear campaign against opposition candidates in an aim to sway public opinion in favor of the ruling party prior to the Dec. 19 election, they said.
The Seoul Central District Prosecutors' Office probing the case prosecuted Won without physical detention, concluding that he had slandered liberal candidates and praised conservative President Park Geun-hye, the ruling party's candidate at the time. She eventually won the election and took office in February.
The outcome of the probe came nearly two months after the prosecution office launched a special investigative team to look into the suspicions.
Won systemically and extensively intervened in domestic politics, not only in violation of the law governing the status of NIS officials but also in violation of the Public Official Election Act, they said.
Won, a close aide to then-President Lee Myung-bak, can face up to 10 years in prison if found guilty of the two laws that strictly ban civil servants from intervening in politics.
The prosecution office, however, said it has decided not to file charges against three former and incumbent agents of the agency's anti-North Korea psychological warfare team as they were just following Won's orders.
Won, who headed the NIS for about four years until March 2013, is accused of abusing his authority with the false belief that the agency is doing its legitimate job in countering Pyongyang's attempts to influence the election results, they said.
Accusations of wrongdoing by NIS agents first surfaced during the presidential election campaign.
The main opposition Democratic Party (DP) accused the agency of trying to influence online debates in favor of Park and against then-main opposition candidate Moon Jae-in.
On April 18, Seoul's Suseo Police Station, which investigated the case for four months, announced that at least two NIS agents allegedly posted online comments criticizing the political opposition ahead of the election.
But police said they could not determine whether the two were part of a much bigger operation by the leadership of the agency to influence the election, as the DP alleged.
Kwon Eun-hee, the lead investigator on the case who had been replaced in the middle of the investigation, claimed a day later that her bosses had intervened in an effort to whitewash the inquiry.
Prosecutors have since taken over the case and concluded that the former intelligence chief had given orders to the agents or been briefed about the agents' alleged activities.
Won allegedly ordered agents to post replies or opinions against certain opposition candidates or parties, they said.
A total of nine NIS agents allegedly posted a total of 1,760 comments or "recommended" or "disapproved of" certain online posts related to the presidential race through more than hundreds of different user IDs between Sept. 19 and Dec. 14 of last year, they said.
Of the 1,760, the prosecution office said that 67 comments were allegedly posted in violation of the election law, the prosecution office said.
Three were critical of Moon and 28 were critical of the DP's North Korean policy, it said. Three posts were in favor of Park and there were other replies or writings that were critical of other opposition candidates as well.
Meanwhile, Kim Yong-pan, the former head of the Seoul Metropolitan Police Agency (SMPA), was also indicted without physical detention on suspicions that he had hampered a police probe into the scandal, prosecutors said.
Kim is accused of abusing his authority by pressuring a police investigation team not to delve too deeply into the case, it said. Kim is also accused of violating the Police Officers Act and the Public Official Election Act, they added.
Another mid-ranking SMPA official has also been indicted without physical detention on charges of permanently deleting data on a computer hard disk ahead of a prosecution raid into the agency's headquarters, they said.
Meanwhile, two former NIS officials have been also indicted without physical detention on charges of handing over private information and informing the DP about the agency's alleged attempt to influence public opinion ahead of the election, they added.
By law, NIS agents are barred from leaking any information they have acquired on duty and may face up to 10 years in prison or receive a fine of 10 million won (US$9,090).
The two were dismissed from the NIS after a tip-off to the DP about the scandal, prosecutors said.
Earlier this week, the prosecution office said it has decided to indict Won, saying that the decision was delayed as it was a difficult case to find relevant proof.
However, the opposition DP has accused Justice Minister Hwang Kyo-ahn of blocking prosecutors from charging the former NIS chief with violating the election law.
The DP also threatened to impeach minister Hwang, saying that he let Won stand trial without detention.
Although the minister denied the allegations, suspicions have risen that there were conflicts between the prosecution office and Hwang over how to wrap up the investigation.
Meanwhile, the Supreme Prosecutors' Office said it will launch a special audit into suspicions that the investigative result were leaked to a major local conservative media outlet.
Earlier in the day, the daily Chonsun Ilbo said in its article that it had acquired investigative notes before the prosecution office officially released the probe outcome.