[1]: 26  He joined free-state militias, spent a winter in Lawrence[1]: 31  and while he did not participate in the Pottawatomie massacre, he was with Brown on other expeditions.

After a brief rest there he was sent to Maryland to rescue another lot of slaves, but by then it was clear the raid was failing and there was no reason for him to follow his instructions.

Cook and five others—Tidd, Osborne Anderson, Owen Brown, Barclay Coppock, and Merriam—attempted to escape northwards into Maryland and Pennsylvania.

Cook was captured—he was briefly America's most wanted man,[1]: 133  and a large reward had been announced, which was later awarded—and taken to Charles Town to face charges.

He faced the same charges John Brown did: murder, inciting a slave insurrection, and treason against the Commonwealth of Virginia.