On May 6, 1463, Jacob Gaon, a tax collector for King Henry IV of Castile, was killed in Tolosa (Gipuzkoa) over a dispute involving rights relating to the foruak/fueros (the charters governing Basque fiscal and institutional relations with central political authority).
Gaon came from a prominent Jewish family in Vitoria-Gasteiz (Araba) and like several relatives worked as a tax collector for the Kings of Castile, to which the province of Gipuzkoa belonged. Indeed, since 1256, Tolosa had enjoyed its own foru/fuero regulating its independent fiscal status within the Castilian political orbit (the result of its strategically important position on the border with the rival Kingdom of Navarre); an agreement that was amended in both 1282 and 1290 to exempt inhabitants from numerous royal tributes.
In May 1463 Gaon went to Tolosa with the aim of demanding the so-called pedido tax, which, the locals claimed, they had never paid before on account of their foral privileges. After threatening them, several inhabitants killed Gaon, beheaded him, and put his head on top of a pillory for all to see. On hearing the news, Henry IV, who was at the time in Hondarribia, also in Gipuzkoa, stopped at Tolosa on his way back to Castile in search of the culprits. Unable to locate them, having been informed that they had taken refuge in a nearby mountain “on the other side of the river,” he settled instead for demolishing the house in which the crime had taken place.
Subsequently, however, on receiving documents demonstrating that the inhabitants of Tolosa had never paid the pedido tax on account of foral law, Henry acknowledged the exemption and issued a pardon.
For an excellent introduction to the Basque foral system, see The Old Law of Bizkaia (1452): A Critical Edition, edited and annotated by Gregorio Monreal.