When he heard of their arrest he nominated Thumeri de Boissise his Ambassador extraordinary to Holland, ordering him to repair thither, immediately, and join Du Maurier the Ambassador in ordinary, in soliciting the States-General in favour of the Accused, and labouring to restore the public tranquillity.
December 12, 1618, they presented to the States-General a Writing from the King, asking that the prisoners might have justice done them; that their judges might be persons impartial and dispassionate; that the States would rather chuse mild, than rigorous measures: "And, said the Ministers, his Majesty will take for a high offence the little regard you pay to his counsels, his prayers, and his friendship, which for the future will be as much cooled as it was heretofore warm in your interest." The States made answer on the nineteenth of December following, that they would act with all the lenity and clemency which justice and the safety of the State would permit; and that they hoped the King would leave it to their prudence.
The French Ambassadors continued their solicitations[88]; but the answer made them March 23, 1619, must have left them no hope: it represented the Prisoners as turbulent men, suspected of very heinous crimes, and almost convicted of conspiring against the Republic, and projecting and attempting to destroy the Union and the State.

This answer was certainly concerted with Prince Maurice, who was highly offended that the King of France should interest himself so much to save men whom he looked on as his declared enemies.

Boissise quitted Holland, leaving Du Maurier alone to act in favour of the Accused.

On Monday morning, May 13, 1619, the Ambassador was informed, that sentence had been passed the Day before, and that Barnevelt was to be executed that day.

He went immediately to the Assembly of the States to get the execution suspended, but was refused audience: he wrote to the States, conjuring them by the regard they ought to have for the King his master, not to spill the blood of a Minister who had served them so faithfully; and, if they would not pardon him, to confine him to one of his country houses, his friends being bound for him; or banish him the country for ever.