The ruling Saenuri Party and the main opposition Democratic Party are renewing their bids to reform the prosecution. Last year, they promoted a comprehensive overhaul of the powerful organization but their campaign bore little fruit due to strong resistance from prosecutors and lack of support from the government.

On Tuesday, the DUP unveiled a 10-point reform plan aimed at ensuring the political neutrality of prosecutors, curbing their power, and strengthening the protection of suspects’ rights.

The plan proposed, among other things, the abolition of the powerful Central Investigation Unit of the Supreme Prosecutors’ Office and the establishment of an independent agency to investigate senior public officials, including Cabinet ministers, judges, prosecutors and lawmakers.

The Saenuri Party has not yet presented a reform agenda. But on Wednesday, Park Geun-hye, the party’s leader and presidential frontrunner, called for a set of fundamental measures, including the introduction of a permanent independent counsel system, to root out corruption involving presidential aides and relatives.

The two parties’ fresh reform bid is welcome as prosecutors have recently shown a growing tendency to use a double standard in dealing with politically sensitive cases. They pounced on opposition politicians or members of the public, while pulling their punches when investigating members of those in power.

For instance, prosecutors launched an investigation swiftly as allegations emerged that the daughter of the late President Roh Moo-hyun might have been involved in an illegal foreign currency remittance scheme carried out in 2009.

Yet they did not act with the same agility to a complaint filed against President Lee Myung-bak’s son in connection with the purchasing of a plot of land in Seoul to build a home for the president’s retirement. Although the complaint was filed four months ago, prosecutors have not yet made any move.

In another example, prosecutors indicted former Prime Minister Han Myung-sook twice in 2010 and 2011 on graft charges before she was elected DUP chairwoman. Her trials are not yet over but prosecutors have thus far failed to establish her guilt. Han is convinced that the indictments were politically motivated.

In contrast, prosecutors stopped short of getting to the bottom of the matter when they investigated the money-for-votes scandal involving the resigned National Assembly Speaker, Park Hee-tae. They found a large sum of money deposited in a bank account of Park’s aide but did not bother to investigate where the money came from.

The political parties’ push for reform was given added urgency by a bombshell testimony dropped by Chang Jin-soo, a former official of the Prime Minister’s Office. Chang is one of the several PMO officials who were sentenced to prison in 2010 for illegal surveillance of a civilian.

Chang reportedly said he destroyed evidence of surveillance before the prosecution launched an investigation. He asserted that he had done so at the instruction of a presidential aide, who had discussed the matter with prosecutors before instructing him.

Chang’s testimony has not been verified yet but his description of the circumstances strongly suggests that the Blue House and the prosecution colluded in destroying evidence to protect presidential aides from being exposed and indicted.

If Chang’s testimony is true, it would further discredit the prosecution and shake public confidence in the nation’s criminal justice system. The prosecution’s primary duty is to administer criminal justice but Chang’s story implies some prosecutors had abandoned it and committed a serious crime themselves.

In the face of public outcry, the prosecution said it would consider reopening its investigation into the case. But the horse has bolted. The crime-busting agency has lost public trust and degraded itself to the point it has become a target of investigation.

When things reach this stage, it is hardly strange that some conscientious prosecutors lose enthusiasm and decide to quit. One of the prosecutors who investigated the money-for-votes scandal offered his resignation, apparently dissatisfied with the way the case was handled. Two more prosecutors recently ended their careers, saying they were frustrated by the prosecution’s failure to maintain political neutrality.

All these things indicate the prosecution has lost the ability to reform itself. Hence, political parties need to intervene to reform it. More than anything else, they need to stop the Blue House from using prosecutors as a governing tool. They also need to make prosecutors subject to public scrutiny to prevent them from wielding their power arbitrarily.