When can lawyers intervene in criminal cases?

Legal analysis: the criminal suspect in a public prosecution case has the right to entrust a defender from the day when he is interrogated for the first time by the investigation organ or takes compulsory measures; During the investigation, only lawyers can be entrusted as defenders. The defendant in a case of private prosecution has the right to entrust a defender at any time. The victims of public prosecution cases and their legal representatives or close relatives, and the parties to incidental civil actions and their legal representatives shall have the right to entrust agents ad litem from the date when the case is transferred for examination and prosecution.

Legal basis: According to Article 46 of the Criminal Procedure Law of People's Republic of China (PRC), the victims of public prosecution cases and their legal representatives or close relatives, and the parties involved in incidental civil litigation and their legal representatives have the right to entrust agents ad litem from the date when the case is transferred for examination and prosecution. The private prosecutor and his legal representative in a case of private prosecution, and the parties to an incidental civil action and their legal representatives have the right to entrust an agent ad litem at any time. The people's procuratorate shall, within three days from the date of receipt of the case materials transferred for examination and prosecution, inform the victims and their legal representatives or their close relatives, the parties involved in incidental civil litigation and their legal representatives that they have the right to entrust agents ad litem. The people's court shall, within three days from the date of accepting a case of private prosecution, inform the private prosecutor and his legal representative, the parties to an incidental civil action and his legal representative that they have the right to entrust an agent ad litem.