In 1582, he was in the service of a Spanish fur merchant, Gaspar de Añastro from Vitoria, who resided at Antwerp.
De Añastro had lost three ships and was tempted by the supposed reward of 80,000 ducats and the habit of the Order of Santiago offered by Philip II of Spain for the assassination of William the Silent, prince of Orange, and being himself without courage to undertake the task, De Añastro (with the help of his cashier Antonio de Venero, a 19-year-old also from Bilbao, and the Dominican friar Antonio Timmerman, from Dunkirk) persuaded his poor accounting assistant Jáuregui to attempt the murder for the sum of 2877 crowns.
Although the pistol was badly designed and malfunctioned, one bullet pierced the neck below the right ear and passed out at the left jaw-bone, but William ultimately recovered.
When William recovered, he asked a merciful execution for the survivors: Venero and Timmerman were garotted on March 28, then decapitated and quartered for public exhibition.
Although William suffered severe injuries, he survived thanks to the care of his wife Charlotte of Bourbon and his sister Mary.