William III had been appointed Stadtholder of Holland and Zeeland in early July, and Johan de Witt had resigned his office of Grand Pensionary on August 4, after having been severely wounded in an assassination attempt.
He and his brother Cornelis were held responsible for the dire straits of the Republic by the common people, who also resented his policy of trying to prevent the elevation of William to the stadtholderate.
When they were both in the jail the building was surrounded by the Hague civic militia, who were fiercely Orangist, because there were rumors that Cornelis would be allowed to escape.
Now Van Banchem, in his official capacity of alderman, made the officers of the militia swear an oath that they would prevent the escape of the De Witts.
After a detachment of federal cavalry had conveniently been withdrawn, the militia led by Van Banchem, Tichelaar, and a silversmith by the name of Hendrik Verhoeff stormed the jail.
After this lynching, William, who probably was not in on the conspiracy to murder the De Witt brothers by van Banchem and the Rotterdam Regent Johan Kievit and his brother-in-law Cornelis Tromp (who had given the signal for the assault on the jail), nevertheless prevented attempts by the authorities to punish those responsible.
His office did not pay a formal salary, but he was allowed to retain certain fines levied, and could also negotiate transactions with suspects to avoid prosecution.
It is not unlikely that the attorney-general exacted some measure of revenge for the events of 1672 when he stringently prosecuted Van Banchem for crimes that were not unusual in those days.