The story relates to the French Revolution, in which a radical journalist, Marat, is murdered in his bath by Charlotte Corday, who believed that his death would end the violence throughout the country. What's interesting to note is that Marat was a friend of Jacques-Louis David, so his portrayal of this scene certainly must have included his own personal feelings about the event.
While the painting is done in a realistic style, it has elements of being idealized, so that Marat's death is almost graceful. His head is resting peacefully on the edge of the tub, and despite being stabbed in the chest, he is still holding a quill in his right hand with which he was writing a letter, which he still holds in his left hand. This along with the dramatic lighting and overall calmness of the scene betrays the actually brutality of the stabbing.
Jacques-Louis David isn't avoiding visual proof that a murder has taken place; the murder weapon, the knife, is seen at the bottom of the canvas to the left of Marat's hand. But in placing it here, David is suggesting that the knife was used as a murder weapon and then dropped to the floor in the aftermath.
Below we have two different paintings in which the person who has died is portrayed as resting on their deathbed. At left we have By the Deathbed, painted by Edvard Munch in 1895. Here the focus is not so much on the person who has died, but rather on those who have come to grieve him. Munch has injected some symbolism here, because while the first four mourners from the left are focused on the person who has died, the fifth mourner is facing the viewer of this painting directly. Note that her face is somewhat skeletal, she represents death, and by looking at the viewer, sends the message that one day, death will come for us as well.
Below at right we have Death of Casagemas, painted by Pablo Picasso in 1901. With this painting, Picasso is mourning the death of his close friend Casagemas, who has committed suicide. Some have suggested that this event contributed to the melancholy that evolved into what was known as Picasso's "Blue Period," in which he painted most of his paintings in a predominantly blue hue.
