Several thousand police officers - 6 000 on Wednesday and another 3 000 on Thursday - were mobilised to raid a sprawling South Korean church compound near Seoul to hunt for Yoo Byung-eun, a fugitive billionaire businessman and member of the church wanted in relation to the deadly ferry sinking in April.
Authorities believe Yoo owns the ship and that alleged corruption may have contributed to its sinking.
The government is offering a $500 000 reward for tips about his whereabouts.
Why so many police?
Police said the sheer size of the compound - about 30 football fields, including a fish farm, cow ranch and a 5 000-seat auditorium - required several thousand officers. Some were deployed outside the complex, the headquarters of the Baptist Evangelical Church, to block possible escape routes while a police helicopter hovered overhead on both days. Dozens of prosecution investigators were also involved.
Police were also worried about potential clashes with church members, some of whom had reportedly threatened to die as martyrs when they refused to open the compound last month. About 200 members who gathered to protest outside the compound Wednesday sang hymns and chanted slogans while pumping their fists in the air.
So far, there have been no reports of violence.
Is this unusual?
In South Korea, it's common to see thousands of police at occasional labour and anti-government protests - often outnumbering the demonstrators. Law enforcement officials say they typically send two or three times as many police as the number of expected protesters to keep order and rein in those who don't follow police instructions.
Protesters have been known to get violent, some of which experts say reflects a deep sensitivity toward government power, a legacy of decades of authoritarian rule of military-backed dictatorships through the 1980s that cracked down harshly on any criticism of the government.
Why are they trying to find Yoo?
Yoo is head of the now-defunct predecessor of the ferry's current operator, Chonghaejin. Authorities believe he still controls the company through a complex web of holding companies in which his children and close associates are large shareholders.
Yoo faces allegations of tax evasion, embezzlement and professional negligence. Officials suspect the sinking may have happened because Chonghaejin illicitly funnelled profits to his family, and failed to spend enough money on safety and personnel.
President Park Geun-hye, whose approval ratings have been hit by the accident, is clearly frustrated that Yoo has not been found. “It makes no sense” that police and prosecutors haven't caught him, she said earlier this week.
In addition to the bounty on Yoo, authorities are offering $100 000 for clues about his eldest son, and one of his daughters was arrested in France late last month.
What did police find during the raids?
Police have confiscated computers, memory sticks, security cameras, documents and automobile navigation systems in a bid to gather clues about Yoo's whereabouts. They also used sniffer dogs and detection devices to detect any possible underground hideout.
They arrested five church members on Wednesday for allegedly providing shelters for Yoo or helping him flee and another one for allegedly trying to obstruct the raid.
What’s the status of the ferry crew?
The sinking of the Sewol left 304 people dead or missing, most of them high school students. The tragedy caused an outpouring of national grief and soul-searching about public safety.
All 15 crew members tasked with navigating the ship have been charged with negligence and failing to do their duty to protect passengers. Four, including the captain, face homicide charges, which could carry the death penalty.
The crew members appeared in court for the first time earlier this week as hostile spectators cursed, shouted and wept behind them. Five employees at Chonghaejin have also been indicted.
The captain and other crew members have been widely criticised for failing to issue orders for passengers to vacate the ship as it listed severely to one side.
Divers are still searching for 12 missing bodies. - Sapa-AP