The National Assembly on Monday launched an investigation into the deadly sinking of the Sewol ferry, about 50 days after the tragedy took place, leaving more than 300 people dead or missing.

The ruling and main opposition parties set the investigation period at 90 days, more than double the norm for a parliamentary probe, which is 40 days. This reflects the magnitude of the tragedy, one of the worst manmade maritime catastrophes in Korea.

During the period, a team of 18 lawmakers will inspect the site of the tragedy together with the representatives of the victims’ families, investigate 18 government agencies and four other organizations, and hold a public hearing for five days.

The 18 agencies include the presidential secretariat and the National Intelligence Service as well as the Coast Guard and the Ministry of Security and Public Administration. Lawmakers will also probe the Korean Register of Shipping and the Korea Shipping Association.

The family of Yoo Byung-eun and the companies under his control, including Chonghaejin Marine Co., the operator of the Sewol ferry, are also on the list of the investigation targets.

Launching the parliamentary investigation, the ruling Saenuri Party and main opposition New Politics Alliance for Democracy pledged to get to the bottom of the matter by conducting a no-holds-barred investigation.

Their resolve is commendable. But don’t expect too much from their investigation. Every time political parties have kicked off parliamentary probes, they have resolved to investigate thoroughly to bring the truth to light.

But there have been few cases where lawmakers went deeper than prosecutors or police to dig out the truth. Often they were less interested in uncovering the truth than in scoring political points for partisan gain.

The latest example is last year’s Assembly investigation into the National Intelligence Service for its alleged meddling in the presidential election in December 2012. The probe ended without getting to the heart of the matter.

The Saenuri Party and the NPAD appeared to be following the established pattern when they quarreled for three days last week over whether to include presidential chief of staff Kim Ki-choon on the list of witnesses.

The wrangling suggested that the two parties were unable to set aside partisan politics in dealing with the ferry catastrophe.

The 18 lawmakers should not forget that partisan politics are also to blame for the disaster. They should thus endeavor to stop bickering and focus on analyzing the ferry tragedy and exploring remedies to prevent similar disasters.