Prosecutors have found evidence confirming the allegations that the National Intelligence Service was systematically involved in the parliamentary and presidential elections last year. Investigators probing the state spy agency said they have newly discovered more than 1.2 million Twitter messages disseminated by NIS agents in the run-up to the two important elections.

The 1.2 million messages were mostly retweets of 26,550 original texts. Investigators suspect that NIS agents had used “Twitterbots” to massively disseminate the original messages. A Twitterbot is a program that automatically retweets a message via fake accounts.

Judging from how the Twitter messages had been spread, NIS involvement in the elections must have been systematic. In fact, that is exactly the conclusion prosecutors had reached earlier this year after investigating the comments posted by NIS agents on portal sites. So they indicted former NIS director Won Sei-hoon on charges of orchestrating the spy agency’s election intervention.

Yet the NIS has thus far strongly denied prosecutors’ findings and protested Won’s indictment. It claims that the NIS agents involved in the scandal posted the comments on their own without any instruction from their superiors. The new Twitter evidence, however, suggests this is not true.

It was only natural that prosecutors asked the court to allow them to rewrite their arraignments against Won and other suspects based on the new evidence. The court is expected to accept the request.

Now, prosecutors need to go deeper to bring into light the spy agency’s entire scheme for election intervention. They should investigate all allegations thoroughly, leaving no doubt whatsoever. At the beginning of the investigation, prosecutors had given the impression of soft-pedaling the case. If they fail to wipe out this impression, they will not only denigrate their reputation but jeopardize the very existence of their organization.

The main opposition Democratic Party and other opposition groups have been pressuring President Park Geun-hye to appoint an independent counsel, expressing their distrust of the Supreme Prosecutors’ Office.

Prosecutors should take the opposition party’s distrust seriously and leave no stone unturned to dig up the truth.

Now, political parties need to discuss how to reform the spy agency to prevent it from meddling in elections. As the ruling Saenuri Party is willing to accept the DP’s demand that they set up a parliamentary panel on NIS reform, there is no reason to delay its establishment.

But the DP’s demand for the appointment of an independent counsel is excessive as prosecutors are still investigating the case, and trials on the suspects are underway. Appointing an independent counsel now would amount to totally negating the SPO. What is the wisdom of taking such an extreme step?