Under Argelander's supervision he produced data for the comprehensive astrometric star catalogue known as the Bonner Durchmusterung, together with fellow student Eduard Schönfeld .
[1] He was awarded his doctorate by the University of Bonn in August 1854 for his dissertation titled "De ascensionibus rectis, a Flamsteedio quadrantis muralis ope observatis".
[2] In 1858 a heliometer previously used by Friedrich Winnecke came into his hands, and was successfully employed in a series of parallax determinations.
At the time of his appointment he married Maria Wilhelmina Amalia, the eldest daughter of Friedrich Argelander.
After leaving Helsinki, Krueger directed the Gotha Observatory (1876-1880), succeeding the recently deceased Peter Andreas Hansen.