South Korean police continued to surround a church compound in Anseong on Thursday, in search of fugitive billionaire businessman, Yoo Byung-eun, believed to be involved in the sinking of the Sewol ferry in April.
Authorities believe Yoo owns the ship, and that his alleged corruption may have contributed to the disaster that left more than 300 people dead of missing.
Police and prosecutors have been after Yoo for weeks and are offering a 500-thousand US dollar reward for information surrounding his whereabouts.
The 73-year-old is a member of a group called the Evangelical Baptist Church, which critics say is a cult.
On Wednesday about 5,000 police officers, some wearing helmets and armed with plastic shields, raided the group's compound in Anseong, just south of Seoul, officers said on condition of anonymity, citing department policy.
Four church members were detained for allegedly providing shelter to Yoo or helping him flee, police said.
Another church member was detained for allegedly trying to obstruct the raid.
It was not clear whether Yoo was at the compound at the time of the raid.
The compound, the size of about 30 football fields, is considered the church's headquarters and thousands of members gather there for services on weekends.
The area contains ranches, fields, a fish farm and an auditorium that can house up to 5,000 people, according to media reports.
Yoo, head of the now-defunct predecessor of the ferry's current operator, Chonghaejin, allegedly still controls the company through a complex web of holding companies in which his children and close associates are large shareholders.
The government has offered a 100-thousand US dollar bounty for Yoo's eldest son, and one of his daughters was arrested in France late last month.
At a news conference in Seoul, South Korean Defence Ministry Spokesman Kim Min-seok said the troops patrolling coastal waters were "keeping a strict watch" on vessels coming in and out of harbours, in case Yoo tries to escape.
The sinking, one of South Korea's deadliest disasters in decades, has caused an outpouring of national grief, and the country is undergoing national soul searching about public safety.
Nearly two months on, 292 bodies have been recovered, mostly students from a high school near Seoul, and 12 people are still missing.
