“Criminal procedure” in a narrow sense, like a trial at criminal court, requires an indictment made by a prosecutor. A prosecutor files an indictment when he or she is convinced of the defendant’s guilt after the investigation, which is conducted as a part of “criminal procedure” in a broad sense, to find substantial truth. Accordingly, for a prosecutor, the goal of finding a substantial truth as an objective of criminal procedure is for the criminal facts found through his investigation to be verified as objective facts. In order to achieve this goal, the prosecutor submits the evidential items he or she has collected through the investigation and proves the defendant’s guilt by examining the submitted evidence.

Consequently, a trial can be a process where the admissibility and weight of evidence submitted by a prosecutor are examined. Here, the trial is based on the “charged facts”, which are substantial truth found as a result of an investigation and the evidence submitted. In order for the facts found by a prosecutor through investigation to be verified as substantial truth through the trial process, the relevance of facts should be sufficiently demonstrated at the investigation stage, prior to indictment.

The prosecutor’s role in order to achieve the goal of the criminal procedure, which is finding a substantial truth through trial, is eventually a persuading the judge by presenting prosecutor’s inference from investigation effectively. For this, the prosecutor has to make judges understand enough about the situation and the main issue in every process, including the testimony of indictments, refute the defendant’s arguments through questioning and organize his or her inference in a convincing way. Furthermore, the most important basic premise in order to be convicted in the criminal court process, where the prosecutor has to prove the evidence, is to present enough evidences to support the facts about the crime, which should be able to be a subject to a prosecution. Therefore, the prosecutor’s inference in the investigation process is very important because the process of ‘the examination of evidence’ is the main point of the criminal court.

Especially in the situation when there is no direct evidence and the prosecutor has to prove the fact only through circumstantial evidences, the prosecutor has to try some tactics of inference so that nobody could doubt from the beginning of the investigation. First of all, the prosecutor has to ensure a number of circumstantial evidences, and from those circumstantial evidences, the prosecutor has to confirm those circumstantial facts through the comprehensive consideration. Through the rules from the observation and measurements, the prosecutor should start oral proceedings after making sure those inferred facts from the through observation and analysis are reasonable. In this process, inferring main facts from the confirmed circumstantial fact and whether deciding those inferred main facts are reasonable, we can consider to apply abduction and retroduction as a philosophical concept.

Prosecutor’s distinct demonstrations and inferences in the investigation encounter the new challenge in trial-base principle and the reality of facilitating the Civic Participation in Criminal Trials Act. It means that, according to court’s reinforcement of trial-base principle, the judges tend to make a decision based on the result of evidence examination in the trial, rather than the record of evidences submitted by investigation prosecutor, hence, there is a possibility that the judge can make a decision while having a prejudice made by defendant or lawyer’s arguments and could not understand clearly on prosecutor’s inference. Also, in the Civic Participation in Criminal Trials Act, the jury, who have the right of preliminary decision, participate in the hearing and through the discussion, they decide whether the defendant is guilty or not, they sometimes make a decision, not reviewing all the record of evidences, only by represented evidences in the trial.

Another major factor that makes an error to the judge or jury’s decision is the uncertainty of legal case. In here, there are judicial factors like, the judge’s prejudice, the lack of prosecutor’s inference during the investigation, and the prosecutor’s lack of expertise and case overloads but there are many non-judicial factors. In order to control the judge’s and jury’s developments of decision, it is necessary to present the record of evidence effectively, use of evidence examination technique according to the criminal procedure code, and make a strategy to intensify the oral proceedings.

In the criminal court process, the interrogation of the witness is the most important process to find a substantial truth. Therefore, it is important for the prosecutor to make an effective ways to interrogate the witness. First of all, as a specific plan for the effective interrogation would be the interrogation which consists of short questions/answers and open-ended questions. Next, the effective use of leading question, leading instinct understanding through questioning and answering about the minor facts. The fifth would be the assertive presentation of the evidence records and the use of visual and auditory materials like Powerpoint presentations. The seventh would be the anticipated interrogation about the lawyer’s questioning and questioning the witness‘s view about the conflicting point between defendant’s and witness’s statements. Lastly, the plan for when the witness change his or her statements and the active use of interviewing witness before the trial. Also, the specific strategy for questioning the defense witness would be firstly, thorough preparation and the active use of leading questions. Thirdly, the questions that could attenuate the trust of witness’s testimony and the disentangle the direct and indirect experience. Lastly, objection to lawyer’s leading questions. Moreover, regarding to prosecutor’s witness questioning, it is also considerable to permit the prosecutor’s witness interview prior to the trial. Furthermore, as trial-base principle is reinforced, the oral proceedings in the trial is getting more important, and as a basic step for the effective oral proceeding would be, having a judge’s point of view, organize the arguments less than three, stick to firm attitudes and speech and use time effectively.

Furthermore, as another arguments of prosecutor’s effective trial practice, the prosecutor’s inference of sentencing hearing would be considered. In order for prosecutor to fully engaged in sentencing hearing, the prosecutor should collect enough presentence investigation. For this process, not only should the prosecutor ensure the victim’s testimony and also, he or she should effectively use the specialized group, such as in the field of criminal psychology. The prosecutor should also think about using video record of the suspect strategically for the investigation. Institutionally, it is considerable to impose the prosecution sentence investigation. Also, this enough-collected data from presentence investigation should be represented effectively in the trial, for this, active victim questioning, intensify the defendant questioning and the effective use of prosecutor’s final arguments.