The so-called illegal evidence refers to evidence that is not legal. The principle of exclusion of illegal evidence refers to the rule that evidence obtained through illegal means should be excluded in criminal proceedings. The criminal procedure law of any modern country prohibits the acquisition of evidence in violation of the law. However, whether illegally obtained evidence can obtain evidence and become the basis for deciding a case is quite controversial in the criminal procedure law community. In summary, there are four main views:

The first view is total denial. It is held that illegal evidence does not qualify as evidence and therefore it is claimed that it cannot be used as evidence. According to the theory of "fruit of the poisonous tree", the use of evidence obtained through illegal means is harmful because it will encourage judicial officials to commit illegal acts, condone the infringement of citizens' rights to privacy, residence and person, and undermine the rule of law. British Lord Chancellor Kilmore famously said: "The procedures of trial activities must be followed, even if - in some exceptional cases - it damages the truth!"

P. The two viewpoints are definitely true. He believes that illegal evidence is qualified as evidence as long as it is verified to be true, and advocates distinguishing between illegal means (the poisonous tree) and evidence obtained by illegal means (the fruit of the poisonous tree). European Judicial Investigator Emerykes is a staunch supporter of this view. He once said: "As long as the truth can be obtained, it does not matter how it is obtained."

The third type The view is a compromise. That is to say: on the one hand, it is believed that illegal evidence does not have the qualification of evidence, on the other hand, it is believed that illegal evidence cannot be completely excluded. Illegal evidence can be regarded as evidence clues, and then converted into legal evidence through legal means.

The fourth viewpoint is the balance of interests theory. It is believed that illegal evidence shall not be used as evidence under normal circumstances, but for cases that endanger major national and social security, based on the balance between national security interests and major social public interests and personal interests, evidence materials obtained through illegal means may also be used Used as evidence in litigation.