What is ironic about daybreak at the chateau of the Marquis in A Tale of Two Cities?

The irony in Chapter Nine of Book the Second lies in the
way that the sunlight actually foreshadows the act of murder that has been committed
during the night. Let us consider the following paragraph from this excellent chapter so
that we can discuss how the irony in it functions:

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Lighter and lighter, until at last the sun
touched the tops of the still trees, and poured its radiance over the hill. In the glow,
the water of the chateau fountain seemed to turn to blood, and the stone faces
crimsoned. The carol of the birds was loud and high, and, on the weather-beaten sill of
the great window of the bedchamber of the Monsieur the Marquis, one little bird sang its
sweetest song with all its might. At this, the nearest stone face seemed to stare
amazed, and, with opened mouth and dropped under-jaw, looked
awe-stricken.

This quote of
course immediately precedes the discovery of the corpse of the Marquis, and thus the
descriptive detail of the water in the fountain turning to blood has ironic
significance. In addition, there is irony in the way that the little bird sang "its
sweetest song with all its might" at the window of the bedchamber of the Marquis, only
to have this excellent song fall on deaf, or dead, ears. The gargoyle faces themselves
ironically appear to be impacted by the act of murder, as they are described as being
"awe-stricken."