This would NEVER have happened in the slaveholding states. In fact, it was Lincoln's strong hint, in a speech given shortly after his second inaugural, that he favored universal enfranchisement of the Negro, that doomed him to death at the hands of Booth. Booth heard the newsies crying on the streetcorner, picked up a newspaper, and made up his mind to kill this "tyrant" who was about to perform the ultimate act of disrespect to the white race.
We can talk about prejudice throughout the U.S. at that time all we want, but the difference in degree was profound.
And most of those who DID actively persecute blacks in the North were themselves unskilled laborers, especially recent immigrants from Ireland, who saw free blacks as a threat to displace them in the workplace.