Prosecutors handle approximately 80,000 criminal matters per year. Most of these are handled in local prosecution offices. The Office of the Prosecutor General handles only a few dozen criminal matters per year. Most of these are cases which fall within his remit by law, such as terrorist offences and offences related to the abuse of freedom of expression. Furthermore, prosecutors working in the Office of the Prosecutor General handle a few criminal matters each year which are of major importance to society due, for example, to the suspect's high position.
In Finland, the pre-trial investigation of criminal offences is handled by pre-trial investigation authorities, the most important of which is the police, which operate within the administrative branch of the Ministry of the Interior. Pre-trial investigation includes the investigation of suspected crimes and their preparation for prosecutors. Furthermore, the Finnish Border Guard, Finnish Customs and the Finnish Defence Forces operate as pre-trial investigation authorities within their own sectors.
During pre-trial investigation, the prosecutor and the pre-trial investigation authority cooperate to ensure that the suspected offence is investigated sufficiently well. Based on the questioning of the parties involved and the evidence acquired during the pre-trial investigation, the prosecutor will complete the consideration of charges, evaluating whether or not to bring charges in the matter, or whether further measures should be discontinued.
In most cases, the prosecutor must press charges if there is probable cause to suspect that a person questioned during a pre-trial investigation has committed an offence. However, even if there was sufficient evidence for pressing charges, the prosecutor can abandon charges by making a decision not to prosecute if legal grounds allowing this can be applied to the case. Such grounds include the offence's being minor or the offender's being young and not giving proper consideration to the act.
Before the matter is referred for consideration of charges, upon the request of the pre-trial investigation authority the prosecutor may order that a pre-trial investigation not be carried out, or that a pre-trial investigation already begun be discontinued. This can be done if it appears likely that the prosecutor would not press charges even if the pre-trial investigation were completed. This procedure is referred to as restriction of the pre-trial investigation.
In more serious criminal matters, the prosecutor can also engage in plea bargaining with the suspect, in which the suspect agrees to plead guilty to the offence. As a result, the prosecutor can propose a more lenient punishment to the court, or waive prosecution for some of the suspected offences.
According to law, the duty of a prosecutor is to impartially, promptly and economically secure criminal liability in a case being considered by him or her, in a manner consistent with the legal safeguards of the parties and with the public interest. A prosecutor must be objective and take account of any evidence that argues against the suspect's guilt in a balanced manner.
A prosecutor is autonomous and independent in his or her decision-making. In any given case, he or she cannot and must not accept instructions or orders from anyone else. Hence, the opinion of the police as to who has committed an offence, for example, is not binding on the prosecutor. Even the Prosecutor General cannot order how a prosecutor should act in a matter in hand. However, the Prosecutor General is entitled by law to take over a case from a subordinate prosecutor, or to assign it to another prosecutor.