Who does Laertes initially blame for the death of his father?act 4 sc 5

Laertes initially suspects that the King has some involvement in his father's death. He bursts into the King's chambers to demand information about his father's death.

Claudius knows there is talk that Laertes might be King and Claudius does not want Laertes to have reason to hate him. The King easily manipulates Laertes into doubting his suspicions by vowing to give up everything he has-even his life-if he in any way had anything to do with Polonius' death.