The prosecution has again disappointed us by coming up almost empty-handed after three months of reinvestigation into the allegations that officials of the Prime Minister’s Office illegally spied on civilians.

Prosecutors did not bother to get to the heart of the scandal, leaving many central questions unanswered. Who was the mastermind behind the illegal surveillance? How deeply was the Office of the Senior Presidential Secretary for Civil Affairs involved in the affair? Had President Lee Myung-bak been briefed about the results of the surveillance operations? Where did the money used to bribe officials to remain silent come from? We still have no clue to these and other questions.

Wrapping up their poorly conducted reinvestigation, prosecutors pressed additional charges against Park Young-joon, former vice minister of knowledge economy who was once considered the president’s right-hand man.

According to the prosecution’s announcement, Park was the mastermind. Now under arrest in a separate corruption scandal, Park was at the top of the secret chain of command that led down to the PMO’s spying team. Prosecutors said the team briefed Park on the outcomes of their surveillance activities. Yet this explanation is hardly convincing.

According to prosecutors, the PMO team conducted surveillance more than 500 times for two years since 2008. The targets included former Supreme Court Chief Justice Lee Yong-hoon, former National Intelligence Service Director Kim Sung-ho, Seoul Mayor Park Won-soon and Gyeonggi Province Gov. Kim Moon-soo.

The list also included such business tycoons as Samsung Group chairman Lee Kun-hee and Lotte Group chairman Shin Kyuk-ho and 10 former and then-incumbent lawmakers.

If Park were the mastermind, as prosecutors would have us believe, they should have found out why he had the PMO team collect information on so many people. Since Park was a close confidant of the president, it is logical to suspect that he gathered information to report to Lee. But prosecutors did not even attempt to investigate the suspicions.

The PMO team is also suspected of having provided its illegally collected information to the Office of the Presidential Chief of Staff and the Office of the Senior Presidential Secretary for Civil Affairs. But prosecutors did not investigate the allegations that the two offices were also involved.

There is also ample evidence to suggest the involvement of higher-up officials of the two offices in the cover-up attempt after the scandal was brought to light by a whistleblower, a former PMO official.

Among the evidence is the 50 million won delivered to the whistleblower by a Blue House official to keep him silent. The official said he borrowed the money from his father-in-law, a testimony that lacks credibility. Yet prosecutors did not press him to tell the truth.

Prosecutors dismissed most of the evidence, showing they had no intention of taking their investigation beyond Park. From the way they conducted the reopened probe, we get the impression that it was aimed from the beginning at clearing top Cheong Wa Dae officials of suspicion rather than zeroing in on them.

Hence prosecutors did not question former Presidential Chief of Staff Yim Tae-hee and the then senior civil service secretary, Kwon Jae-jin, who is currently the minister of justice. In particular, they must have found it awkward to question Kwon as he is the minister who governs the prosecution.

As the prosecution’s reinvestigation has shed little new light on the scandal, another investigation, whether by an independent counsel or by a special parliamentary probe team, has become inevitable. The blame for this goes to the prosecution that has bungled the investigation twice.