Flawless Plan - S1.E16

An unidentified young woman was found dead on the seashore. She had two blows to the head, one fatal, and was wearing a man's shirt. Superintendent Orhan and his assistant Selim soon learned that the victim was Pelin Onur, a shareholder of Onur Real Estate Investment Trust, who had been kidnapped for ransom three days earlier. Fearing that her sister would be harmed, Pelin's sister and the other shareholder of the company, Gönül Onur, had paid the two million liras demanded by the kidnappers.
 Why did the kidnappers kill Pelin even though they got what they wanted? While Superintendent Orhan and his assistant Selim were trying to find Pelin's killer, a mysterious witness was after the money taken by the kidnappers.