Where in the world are detectives allowed to intervene in criminal cases?

Private detective agencies have experienced the development of 100 years abroad, and criminal investigation has gradually developed into legal private detective agencies or large-scale investigation companies and private security companies.

It is reported that from Europe and America to Northern Europe, South America, Oceania, and even some Asian and African countries, such as the Philippines, Thailand, Malaysia, Singapore, Zambia, Zimbabwe, etc., many countries have private detective companies, which not only develop rapidly, but also have a broad market and their status is recognized by laws of various countries. Even some private detective agencies cooperate with state and state judicial organs, and the state pays private detective companies to investigate relevant information and events for them.

During the American Civil War, Pinkerton and his detectives directly served the country and set up an organization to collect military information of southern separatist forces for President Lincoln's federal army. It is this system that makes Pinker, an excellent private detective agency, a large investigation company with branches in many countries and a model of detective industry. The legal basis of foreign private detectives is mainly the law. For example, there is a law in the United States that both parties and agents can investigate and collect evidence like people with evidence, and no one will refuse, otherwise they will be punished by law.