The prosecution is set to question Rep. Cho Hyun-yong of the ruling Saenuri Party over allegations that he took hundreds of millions of won in bribes from a parts supplier when he chaired the board of the Korea Rail Network Authority from 2008 to 2011. It also suspects Cho of taking bribes after he was elected to the National Assembly in 2012.

The allegation against Cho is developing into a bribery scandal of great magnitude as the prosecution expands its inquiry into the case. Cho is one of several politicians the prosecution suspects of taking bribes from Sampyo E&C and other parts suppliers.

The sordid ties among politicians, the government-run corporation and its suppliers were first exposed when a high-speed train derailed in 2011. The parts supplier AVT became the target of a criminal investigation when the rail-fastening system it had supplied was found to be faulty.

The investigation, which had since been going on and off, took a new turn when Kim Kwang-jae, a former president of the government-run Korea Rail Network Authority, took his life last month. He had been accused of taking bribes from AVT for awarding the supplier with contracts. Prior to his suicide, the prosecution arrested a deputy spokesman of the Saenuri Party and an auditor with the Board of Audit and Inspection on charges of taking bribes from AVT.

Now the law-enforcement agency is expanding its inquiry into the bribery case, targeting more former and incumbent members of the National Assembly’s Land, Infrastructure and Transport Committee for prosecution. It arrested Cho’s chauffeur and a friend of his, through whom the lawmaker allegedly took bribes from Sampyo E&C. Cho had been a member of the powerful committee until recently.

The prosecution will have to go the extra mile for a watertight investigation and take action against all suspect politicians. Few of the suspects deserve any leniency, given that bribery tends to compromise safety and may lead to the death of hundreds of people, as was the case with the April sinking of the Sewol ferry.

The National Assembly is called on to assist the prosecution in severing rotten links among politicians, public officeholders and businesses by immediately passing the Kim Young-ran bill, a tough anticorruption bill. It has no reason to delay its passage.