The Committee of Vigilance promptly arrested the Knapp brothers and sent them to the Salem Gaol, their cells not far from those occupied by the Crowninshields.

That same evening, after stealing what he believed to be the will, Joe Knapp “unbarred and unscrewed” a window in Captain White’s house.

After just five hours of deliberation the jury accepted Webster's contention that Frank Knapp was a principal to the crime and convicted him of murder.