The Office of the District Attorney also called: The Office in First Instance, is part of the Public Prosecutor's Office and is responsible for the detection and prosecution of criminal offenses.

The Public Prosecutor has the authority and direction of investigations done by the police. The Public Prosecutor determines whether he wants to submit a criminal case to the Judge, or not (principle of opportunity). The Public Prosecutor can also offer the suspect a proposal, to handle the case differently (for example by a conditional discharge or a transaction). If the Public Prosecutor decides to submit the case to the Judge, he acts as Accuser. During the trial in the courtroom, the Public Prosecutor demands a punishment. The court ultimately decides whether, and if so, what punishment is imposed.

The Public Prosecutor must always follow a strict procedure as laid down in the Law. The judge is to check whether the rules are being applied properly. In the courtroom the suspect sees the Public Prosecutor in his role as Accuser. Wearing a black gown with white bands. During the hearing the Public Prosecutor explains the reason why the person is going to trial. Subsequently, the Judge questions the defendant about the case. The Public Prosecutor also gets the opportunity to ask questions, as does the suspect's lawyer. Thereafter, the Public Prosecutor renders his requisitory, a closing speech in which he tells the Judge what he thinks of the case and demands a punishment. That can be a financial punishment, a community service sentence or a jail sentence.

If the Public Prosecutor is speaking, he always does that in a standing position. The Judge, who sits right across from the suspect, will always remain seated. For that reason, members of the Public Prosecution are also called the standing Magistrates. The Judges are part of the sitting Magistrates.

The Public Prosecutor should also ensure that decisions of the criminal courts are carried out. For example, he sends the police on the road to pick up people, who still have to serve a prison sentence, if they do not show up. Fines can be paid at the counter of the Office of the Public Prosecutor's Office.