The inquisition had been on the minds of both Gregory IX and Frederick II long before its formal establishment in the Empire at the end of the 1220s and the beginning of the 1230s. Before becoming pope, Cardinal Ugolino of Ostia persuaded Frederick to promulgate a first set of imperial decrees against heretics on the day of his coronation as emperor in 1220. In 1224 Frederick re-inforced legislation against heretics in Lombardy. In turn, Gregory IX, after becoming pope, reconstituted the inquisition in Lombardy in 1227, and at the same time sent Conrad of Marburg, previously a crusade preacher in papal service, as inquisitor to Germany. But despite Conrad of Marburg's efforts, the inquisition in Germany was underdeveloped in the late 1220s. The effective running of the inquisition required close collaboration between the secular and the ecclesiastical powers. Only the latter could conclusively decide who was and who was not a heretic and only the former was in a position to punish those convicted. This fact was brought home to the pope most forcefully in 1227–8, when the conflict surrounding the allegedly heretical Drenther peasants took on warlike dimensions. After the murder of Bishop Otto II of Utrecht by the Drenthers, Willibrand of Oldenburg was elected as his successor in 1227. According to the Gesta Episcoporum Traiectensium, Willibrand was chosen because of his close family ties with the counts of Holland and Guelders, who were among the major opponents of the Drenthers, and because of his acquaintance with Emperor Frederick II. Willibrand was expected to be a strong and resourceful avenger and defender of the episcopal rights and honours.