High-level police officials reportedly attempted to whitewash an investigation last year into an intelligence agent accused of interfering in the presidential election.

On Thursday, Seoul’s Suseo Police Station announced the result of its 128-day probe into the case, referring two National Intelligence Agency officials and a civilian to the prosecution, recommending indictments.

According to a Yonhap News report Friday, a police officer familiar with the investigation revealed the Seoul Metropolitan Police Agency interfered with the local police’s initial investigation into one of the agents in December after the opposition Democratic United Party filed the complaint.

According to the officer, the Seoul police reduced the number of key words used to track the NIS agent’s online activities to four from the 78 Suseo station requested, and announced less than three days later that no evidence of wrongdoing was found.

In addition, the Seoul police agency is reported to have asked for the NIS agents permission in analyzing various files found on her computer.

“Results could not have been produced that quickly using the 78 key words (Suseo station) submitted for analysis. Suseo station’s team was stupefied by the feeling of having been duped,” said the police officer.

In the run up to the Dec. 19 election, the NIS agent identified by her surname Kim was accused of posting online comments on politically sensitive issues in an attempt to influence public opinion.

Additional investigations have unearthed evidence that another agent and a civilian were involved, and the police have now transferred the case to the public prosecutors’ office, which plans to set up a special investigation team to look further into the case.

On Thursday, the police said the two NIS officials had violated a law on the agency, but not the Public Official Election Act.

The results of the investigation riled the DUP.

“The DUP denounces the police for its incompetence and political bias, and will make the police answer for investigating a case that seriously damaged the basis of a nation,” DUP spokesperson Rep. Kim Hyun said Friday, claiming the police had downplayed the case in anticipation of the government’s stance.

For its part, the ruling Saenuri Party called for the public prosecutors to thoroughly investigate alleged wrongdoings of the DUP, referring to the extended stand-off between DUP officials and the NIS agent at her home on Dec. 11.

“If the police and public prosecutors do not conduct proper investigations in consideration of the opposition party, the Saenuri Party will not stand idly by,” Saenuri Party floor spokesman Rep. Lee Cheol-woo said.

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