What work of art tells story a man who was murdered in his bath?

You're likely thinking of "The Death of Marat" by Jacques-Louis David.

This famous neoclassical painting depicts the French revolutionary leader Jean-Paul Marat, assassinated in his bath by Charlotte Corday, a young Girondin supporter.

Here's why it fits your description:

* Murder in the Bath: The painting depicts Marat slumped over in his bath, with a dagger protruding from his chest, a clear indication of his murder.

* Story of a Man: The painting portrays Marat as a martyr for the revolution, highlighting his commitment to the cause and his tragic demise.

* Historical Significance: The painting became an iconic symbol of the French Revolution and the violence that accompanied it.

While there might be other works of art that depict a man murdered in his bath, "The Death of Marat" is the most famous and readily identifiable example.