A more thorough explanation:

An investigating magistrate is a quasi-judicial officer responsible for examining and ruling on certain aspects of a criminal proceeding before it comes before a judge. This officer is a kind of quasi-judge standing halfway between the prosecutor and the regular court. The investigating magistrate is responsible for investigating criminal charges and certifying them as deserving trial in court.

For example, in some countries, before a criminal charge may be brought before the regular courts, it must be investigated by a special official, the investigating magistrate. The investigating magistrate is responsible for examining the evidence and determining whether there is enough evidence to proceed with a trial.

The role of the investigating magistrate is controversial because the certification of a case for trial tends to confirm the criminal charge against the suspect, creating a strong presumption of guilt. This can be a threat to the integrity of the trial in open court because the accused has had a kind of half-trial in advance of the real trial, conducted by a kind of half-judge who acts essentially as an inquisitorial court.

Overall, the investigating magistrate is an important part of the legal system in some countries, but there is always some concern about its potential for abuse.