This July 24 will mark National Private Investigators Day. The day honors the success and importance of the profession and highlights the changing needs and requirements for private investigators to do their work.

National Private Investigators Day was kicked off nearly 20 years ago by Bob Mackowiak, then owner and publisher of PI Magazine. Back then it was held in October but the day lost a following. Then in 2014, Arthur Athas of Private Investigators Now in Australia contacted the Associates in Forensics Investigations agency to relaunch the day. July 24 was chosen in honor of the birthday of Eugene Francois Vidocq, a French criminal and criminalist turned private investigator who founded the first know detective agency in 1833. According to sources, his reputation is credited with shaping the way law enforcement and investigations are carried out today.

At the start, private investigators often took on a more law enforcement focused role that their clients felt the police either weren’t willing to handle or couldn’t handle at the time. They often dealt with labor, employment and employee issues. Wealthy clients in other countries used private investigators to keep their labor force in line and stop revolts usually by force.

In 1850, Allan Pinkerton established the Chicago-based Pinkerton National Detective Agency as a security force and detective agency. Pinkerton had become famous when he foiled a plot to assassinate then President-Elect Abraham Lincoln. Pinkerton’s agents performed services which ranged from undercover investigations and detection of crimes, to plant protection and armed security. Allan Pinkerton hired Kate Warne in 1856 as a private detective, making her the first female private detective in America.

Among the Agency’s main customers were the railroads, which had to contend with outlaws who robbed trains of cargo and passengers of personal possessions. In the mid-1800s, there were no federal authorities to chase outlaws across state and territorial lines, and local law enforcement was too poorly equipped to pursue fleeing gangs very far. The job often fell to crime victims and their hired agents. Pinkerton agents were also hired to track western outlaws Jesse James, the Reno brothers, and the Wild Bunch, including Butch Cassidy and the Sundance Kid.

The first real licensing for private investigators was in 1915 in California. From there other states began adopting similar licensing requirements. Although, even now, not every state requires a license. Closer to the 1920s, with the country’s booming wealth, more average citizens began using the services of private investigators for a variety of investigative needs.

Over time the industry has changed to meet with the steady demand of ever-changing work. Issues like divorce, infidelity, child custody, insurance fraud and criminal defense work has brought changes to the field and also how investigators conduct their work.