The public prosecutor traditionally wielded little authority within the criminal justice system in New York during the nineteenth century. Private citizens initiated the majority of criminal cases and since judicial proceedings depended solely on the willingness of the complainant to carry the prosecution forward, few cases came to trial. The rapid growth of the city in the late nineteenth century, the concomitant increase in crime, and decisions by the state courts to strengthen the power of the public prosecutor all led to a rapid decline of private prosecutions and the emergence of the district-attorney as a central figure within the criminal justice system. The district-attorney, who previously had done little more than arrange the court calendar, now had the authority as a representative of the state to bring cases to court and to exercise his discretion to prosecute.
The corruption of New York politics under Democratic Party control in the late nineteenth century allowed each incumbent district-attorney to use his office to reward friends and to punish enemies. The district-attorney now rarely used his position in the unbiased pursuit of justice but more typically colluded with ward politicians and police captains to exact bribes and favors from saloon keepers and brothel owners who expected to avoid prosecution in the courts. The initiative taken by such private organizations as the Society for the Prevention of Crime and the appearance in the 1890s of a political reform movement dedicated to eliminating corruption led to the eventual defeat of the Democratic Party machine.
William Travers Jerome, as a judge on the Court of Special Sessions, allowed Charles Parkhurst, pastor of the Madison Square Presbyterian Church, to bring private prosecutions of casino owners before his court. Theodore (Teddy) Roosevelt, then governor of New York, lent his support to the reform campaign and the publicity attendant on Parkhurst’s efforts to prosecute corrupt officials resulted in the defeat of the Democratic Party and the victory of the Fusion campaign. Jerome won election as the reform candidate for district-attorney in 1901 and used the power of his office to vigorously combat gambling and prostitution. The Democratic machine regained control of the city in 1904 but Jerome remained the district-attorney until 1909. He transformed the office of district-attorney by establishing its political independence, ensuring that the decision to prosecute is determined solely by the preponderance of evidence of wrongdoing.