The most famous example of this was the Homestead Strike of 1892, when industrialist Henry
Clay Frick hired a large contingent of Pinkerton men to regain possession of Andrew Carnegie's
steel mill during a lock-out at Homestead, Pennsylvania. Gunfire erupted between the strikers
and the Pinkertons, resulting in multiple casualties and deaths on both sides. Several days
later a radical anarchist, Alexander Berkman, attempted to assassinate Frick. In the aftermath of
the Homestead Riot, several states passed so-called "anti-Pinkerton" laws restricting the
importation of private security guards during labor strikes. The federal Anti-Pinkerton Act of 1893
continues to prohibit an "individual employed by the Pinkerton Detective Agency, or similar
organization" from being employed by "the Government of the United States or the government
of the District of Columbia."
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 Pinkerton agency's
logo, an eye embellished with the words "We Never Sleep," inspired the term "private eye."
It was not until the prosperity of the 1920s that the private investigator became a person
accessible to the average American. With the wealth of the 1920s and the expanding of the
middle class came the need of middle America for private investigators.
Since then the private detective industry has grown with the changing needs of the public.
Social issues like infidelity and unionization have impacted the industry & created new types of
work, as has the need for insurance &, with it, insurance fraud, criminal defense investigations
and the invention of low-cost listening devices. It has also paved the way for specialization in
the field of investigation. For instance, there are investigators whose work are centered on, say,
people who are trying to cheat motor insurance companies by staging accidents.
In a number of countries, a licensing process has been introduced that has put criteria in place
that investigators have to meet: in most cases, a clean criminal record. This has combined with
modern business practices that have ensured that most investigators are now professional in