The Non-Canon Expert explains why Dooku had a secret collection of lightsabers that once belonged to Jedi who had fallen in battle, and describes why this lightsaber collection was important to his eventual fall from Jedi Master to Sith Lord.
This is a Legends story for Dooku from a number of sources, including the novel Labyrinth of Evil and the comic Jango: Open Seasons. I hope that you enjoy it!