All this happened between the years 1834 and 1838.

Afterwards Dr.Emerson brought Dred Scott and his family back to Missouri.

In this suit they now claimed freedom, because during the time of residence with their master at these military posts slavery was there prohibited by positive law; namely, at Bock Island by the ordinance of 1787, and later by the Constitution of Illinois; at Fort Snelling by the Missouri Compromise acts of 1820, and other acts of Congress relating to Wisconsin Territory.
The local court in St.Louis before which this action was brought appears to have made short work of the case.

It had become settled legal doctrine by Lord Mansfield's decision in the Somersett case, rendered four years before our Declaration of Independence, that "the state of slavery is of such a nature that it is incapable of being introduced on any reasons, moral or political, but only positive law....

It is so odious that nothing can be suffered to support it but positive law." The learned chief-justice therefore ordered that Somersett, being claimed as a Virginia slave brought by his master into England, when it was attempted to carry him away against his will, should be discharged from custody or restraint, because there was no positive law in England to support slavery.