SEOUL, South Korea (AP) — South Korea has boosted to half a million dollars a reward for tips about the mysterious billionaire who the authorities believe owns a ferry that sank last month, police said Monday. Meanwhile, five employees at the ship’s operator have been indicted.

The ten-fold increase in the reward comes as officials struggle to find Yoo Byung-eun on allegations of tax evasion, embezzlement and professional negligence. Prosecutors have said that a failure to spend enough money on safety may be a reason for the April 16 sinking.