This demonstrates how badly you have learned your history. The Northern states had an obligation to return all escaped slaves. It was a *LAW* written directly into the US Constitution.
Look up Article IV, Section 2 and read what it says.
It says fugitive slaves must be returned. Refusing to do that is violating constitutional law.
The "fugitive slave law" passed by congress merely said the same thing as Article IV, Section 2 said.
and the Dred Scott Decision, which tried to extend Slavery into the North.
The Dred Scott Decision was never reversed and was a proper interpretation of the law at the time that decision was handed down. The Dred Scott Decision was set aside by the 13th amendment.
George Washington routinely kept slaves in Pennsylvania long after Pennsylvania declared itself "free".
And Jackson was a son of the South. MANY Southerners fought for the Union.