Abstract
Considering the requirements and duties that the investigator or judge must observe in terms of respecting
the rights of the defendant and individual freedoms, as well as in terms of respecting the dignity of the
judiciary in investigating and gathering evidence, violation of these requirements and duties in some cases
can lead to unreliability of evidence or invalidity of research. For example, one of the most common and
accessible ways of detecting a crime is the defendant’s confession through torture, reluctance and
coercion of officers and agents, that even if it leads to obtaining other material evidence that confirms
their authenticity, it cannot be relied on and the material evidence obtained. Other cases of annulment of
investigations include annulment of investigations conducted by persons other than judicial officers,
annulment of investigations conducted in the event of deprivation of access to a lawyer, and nonobservance
of the requirements related to the preparation of the minutes of the interrogation sessions and
the regulations related to the confession and testimony. Considering the existing cases, some criteria can
be stated for the annulment of investigations, which are: gross violation of fundamental rights and
freedoms or invasion of the most private privacy, prohibition of interrogation methods involving the risk
of obtaining false confessions or information, prohibition of unfair crime detection methods or contrary to
the dignity of the judiciary. Therefore, as a general rule, it can be said that the violation of the most basic
rights of the defendant in the preliminary investigation stage, assuming non-compliance with legal
requirements, invalidates the preliminary investigation and its implementation is not limited to
disciplinary action or criminal prosecution. As a result, in order to respect and protect the rights of the
defendant and the correct methods of obtaining evidence, it is necessary to clarify the provisions related
to the request for annulment of the preliminary investigation in the Iranian criminal procedure. Deviation
from the principle of openness of proceedings, except in cases permitted by law, which are prescribed
only in democratic conditions and as a result of the balance of conflicting interests and values, is
considered a violation of the principles of fair trial and disregard for the fundamental rights of individuals.
Despite some initial assumptions that generally equate the components of a fair trial to the rights of the
defendant, a public hearing also entails benefits to society. Therefore, the "individual right of the
defendant" and the "public interest of society" should be defined and explained as the theoretical basis
and justifications for the openness of criminal proceedings. This research, after designing and preparing
the topics, describes the theoretical foundations of the openness of the trial

Key words: Defendant's Rights, Preliminary Investigation, Fair Trial, Justice, Principle of Equality