Thomas slaps his wife Maria once in the face at their place of residence in Walvis Bay. Later the same day, Thomas throws a stone at Maria, hitting her on the back of her hand. Thomas, in an act of retaliation against Maria, then kills his 10 months old daughter by hitting her head against a concrete slab.
Identify the crimes committed by Thomas and discuss the given scenario in light of the applicable criminal law principles. Determine the principle on which the courts must rely in order to reach a just and fair sentence that serves both the offender and society's best interests.