Prosecutors investigating the sinking of South Korean ferry Sewol seized documents and recordings from a coast guard office in Mokpo on Monday.
The seizure is part of investigators' efforts to expand the probe into how the coast guard and other rescuers responded after learning the ferry was sinking.
A senior prosecutor said they would do the same at an emergency call service centre that received a call from a student on the ship reporting the sinking.
Prosecutors also plan to question officials from the company that maintained and inspected life rafts and safety facilities on the ferry.
The prosecutor said they will also focus their investigations on other factors that could have affected the ship's sinking, including cargo stowage and an earlier remodelling of the ship.
Divers on Monday renewed their search for more than 100 bodies still trapped in the ferry after weekend efforts were hindered by bad weather, strong currents and floating debris clogging the ship's rooms.