What is a Preliminary Investigation?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 04 August 2018
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A preliminary investigation is an inquiry conducted by law enforcement representatives to gather more information about an allegation. The purpose of the inquiry is twofold: it is designed to determine whether or not a crime was committed and to identify a suspect or confirm a suspect's identity. Using the results of the inquiry, a decision is made about whether or not to move forward with a full investigation, formal accusation, and trial.

The process starts when someone files a complaint. A police officer takes down details from the complainant, taking special note of facts that can be verified and people who may be related to the case. Once a complaint has been filed, a determination about whether or not it is valid must be made to rule out situations in which allegations are clearly false. Then, a preliminary investigation can be conducted.

In the investigation, steps are taken to verify information in the complaint, and to expand upon that information. This can involve collecting evidence, interviewing people, and taking other investigative steps. All of this information is pulled together in a report. The report can indicate whether or not the investigator agrees that a crime was committed and it may identify a suspect.


There may be situations in which there is clear evidence of a crime, but no suspect. A person cannot be accused of the crime because no one has been identified, but officers can continue to investigate. They can also keep information about the crime on file in the event that more information comes in at a future date, allowing them to reopen the investigation and potentially to bring someone to trial.

A preliminary investigation can indicate that a crime occurred and that someone is a suspect, but it may also reveal that there is not enough evidence to move forward with a prosecution. In this situation, a prosecutor may recommend waiting on a trial and continuing to investigate the case to see if evidence can be collected to support the case. This decision is made with the understanding that, while the case could be brought to trial, it would be a fruitless endeavor because the outcome of the trial would inevitably be acquittal.

Complainants can check on the status of a investigation. The officer the complainant meets with usually provides contact information to allow him or her to follow up on the complaint.


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Discuss this Article

Post 8

This is brilliant information, but how can you refer this to an investigation such as the lab. I would really like it if someone can help me.

Post 7

Thank you very much. This article will surely help me on my report on Monday. Good luck to me. I am a criminologist.

Post 5

This is a personal experience of a local, a female Ll.B. holder reported a crime to the Philippine National Police (PNP) just last week and reading a published letter by Hustisya at the Bar Ops yesterday piqued a closer look into the conduct of PI as worded in the Rules of Court as amended. It's PI before a complaint, in my case, as of my last visit.

Post 4

A preliminary investigation sounds like it could be a slow moving and unbearable time for someone who has had something horrible happen to them or their family. If someone did something bad to me, I would want them taken into custody immediately. I would be worried that they would have the chance to get away during an investigation.

I understand that investigations have to happen to protect innocent people, but it would be very hard to wait.

Post 3

What is the difference between a preliminary investigation and a preliminary hearing? Is the investigation just a gathering of facts, and a hearing more of a formal questioning?

I've heard both of these terms many times before, I just never really understood the difference.

Post 2

This sounds like a good system to me. Can you imagine what it would be like if every complaint that someone made to the police was immediately brought to trial? It would definitely waste a lot of time and money.

It's good that we have preliminary investigations in order to avoid this, and also to protect innocent people. Anyone can make a complaint about someone else. A preliminary investigation makes it possible for people who are completely innocent and falsely accused to avoid having to go through a trial.

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