How to get the criminal investigation file number after an arrest in Mexico

After someone is arrested in Mexico, one of the first things the family urgently needs is the criminal investigation file number (número de carpeta de investigación). Without this number it is extremely difficult to follow the case, request information, or have a lawyer properly intervene before the prosecutor.

The investigation file number is the official reference that the Mexican justice system uses to identify every criminal case. All documents, decisions, and communications related to the arrest will be linked to that number. Families who do not obtain it early often face delays and confusion.

Why the investigation file number is so important

With the file number, a lawyer can locate the exact prosecutor assigned to the case, request copies of the investigation file when legally allowed, monitor deadlines and important hearings, and file legal motions on behalf of the detained person. Without the number, the family and the lawyer waste time trying to identify the correct case among many others processed every day at the prosecutor’s office.

How to obtain the investigation file number

The most direct way is to go in person to the prosecutor’s office (Fiscalía) where the person was presented after the arrest. Once there:

• Ask for the area that handles new arrests or “control de detenciones”.
• Provide the full name of the detained person and the approximate date and time of the arrest.
• Show your official identification and, if requested, proof of family relationship.
• Politely but firmly request the investigation file number and the name of the assigned prosecutor.

Legal Framework

According to the Código Nacional de Procedimientos Penales (CNPP), the investigation stage begins with the presentation of a complaint or with the detention of a person (Article 211). The detained person and their defense have the right to access the records of the investigation at the appropriate stage (Article 219). Article 113 of the CNPP also recognizes the right of the detained person to communicate with a family member. The Mexican Constitution (Articles 16 and 20) protects the right to liberty, to be informed of the reasons for the detention, and to an adequate defense.

Official information about the rights of detained persons is available on the Mexican government portal: Cartilla de Derechos de Personas en Detención – gob.mx.

Common difficulties families face

It is not unusual for staff to be reluctant to give information to family members, especially if they arrive without a lawyer. Having a criminal defense lawyer present greatly increases the chances of obtaining the number quickly and correctly. Do not accept vague answers. Insist on getting the exact file number in writing if possible.

You can learn more about the early stages after an arrest in our article: The Police Arrested Me in Mexico: Your Rights & Next Steps.

Practical tips

Go as early as possible in the morning. Bring multiple copies of identification documents. If the detained person is a foreigner, also bring the passport information. Write down the names of the people you speak with at the prosecutor’s office. If the first attempt fails, return with a lawyer.

Final recommendation

Obtaining the investigation file number is one of the first concrete actions a family can take to protect a detained relative. The sooner you have it, the sooner a proper legal defense can begin.

For specialized criminal defense in Tijuana and Baja California, visit our page on Criminal Lawyers in Tijuana.

Contact Justicia Transparente immediately. Our criminal defense team can locate the investigation file, communicate with the prosecutor, and start protecting your family member’s rights from the first hours after the arrest.