A commission was appointed by the high court of Holland, acting in conjunction with the States of the Provinces, to try the offenders.  Among the commissioners were Adrian van der Werff, John van der Does, who had been military commandant of Leyden during the siege, Barneveld, and other distinguished personages, over whom Count Maurice presided.  The accused were subjected to an impartial trial.  Without torture, they confessed their guilt.  It is true, however, that Cosmo was placed within sight of the rack.  He avowed that his object had been to place the city under the authority of Leicester, and to effect this purpose, if possible, without bloodshed.  He declared that the attempt was to be made with the full knowledge and approbation of the Earl, who had promised him the command of a regiment of twelve companies, as a recompense for his services, if they proved successful.  Leicester, said Cosmo, had also pledged himself, in case the men, thus executing his plans, should be discovered and endangered, to protect and rescue them, even at the sacrifice of all his fortune, and of the office he held.  When asked if he had any written statement from his Excellency to that effect, Cosmo replied, no, nothing but his princely word which he had voluntarily given.

Volmar made a similar confession.  He, too, declared that he had acted throughout the affair by express command of the Earl of Leicester.  Being asked if he had any written evidence of the fact, he, likewise, replied in the negative.  “Then his Excellency will unquestionably deny your assertion,” said the judges.  “Alas, then am I a dead man,” replied Volmar, and the unfortunate deacon never spoke truer words.  Captain de Maulde also confessed his crime.  He did not pretend, however, to have had any personal communication with Leicester, but said that the affair had been confided to him by Colonel Cosmo, on the express authority of the Earl, and that he had believed himself to be acting in obedience to his Excellency’s commands.

On the 26th October, after a thorough investigation, followed by a full confession on the part of the culprits, the three were sentenced to death.  The decree was surely a most severe one.  They had been guilty of no actual crime, and only in case of high treason could an intention to commit a crime be considered, by the laws of the state, an offence punishable with death.  But it was exactly because it was important to make the crime high treason that the prisoners were condemned.  The offence was considered as a crime not against Leyden, but as an attempt to levy war upon a city which was a member of the States of Holland and of the United States.  If the States were sovereign, then this was a lesion of their sovereignty.  Moreover, the offence had been aggravated by the employment of United States’ troops against the commonwealth of the United States itself.  To cut off the heads of these prisoners was a sharp practical answer to the claims of sovereignty by Leicester, as representing the people, and a terrible warning to all who might, in future; be disposed to revive the theories of Deventer and Burgrave.