In Shakespeare's Hamlet, the deaths of all of the characters you mention are the result of Claudius' murderous conniving.
Claudius talks Laertes into killing Hamlet to avenge Polonius' death. They arrange for a friendly game of "sword play," but Laertes poisons the tip of one sword as part of the their plan to dispose of Hamlet.
As a backup plan, Claudius also has wine at the event, and allegedly drops a large pearl in the cup to show his faith in Hamlet's abilities to win, saying he will have the pearl as a reward: the pearl, however, is also poisonous.
Stay, give me drink. Hamlet, this pearl is thine;
Here's to thy health.
Drum, trumpets, and shots. A piece goes off.
Give him the cup. (V.ii.283-285)
As the sword play begins, Hamlet acts lighthearted, even though he expects treachery from some source. Laertes loses his sense of "play" and becomes aggressive with Hamlet, drawing blood with the poisoned sword.
In a scuffle, the swords are exchanged and Hamlet, unknowingly, ends up with the...
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