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How to Conduct Criminal Investigations

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Criminal investigators gather facts and examine evidence of crimes committed at local, state and federal levels. The United States FDA Investigations Operations Manual reports that the purpose of the criminal investigation is to obtain information, document the facts and report the results for possible prosecution. In order to perform an effective criminal investigation, you must know the basic guidelines of the investigative process. While types of criminal cases may vary, the following procedures can be followed to help the prosecution prove the case beyond a reasonable doubt.

Gather Evidence

Identify and locate suspects and perform criminal records queries on all targets of the investigation. After you identify a suspect, create an investigative strategy to prove the case.

Collect all important evidence regarding the suspect’s culpability. Use this evidence to develop a timeline of the alleged crime.

Make sure that all evidence follows the proper chain-of-custody requirements. Physical evidence such as fingerprints or blood samples should be immediately packaged, sealed and delivered to an evidence custodian.

Interview Witnesses

Interview anyone who has direct knowledge regarding the alleged crime.

Take detailed notes during the interview.

Avoid leading questions. Use free narrative to allow the interviewee to provide an account of the incident without prompting.

Perform Surveillance

Monitor the suspect through visual surveillance or with assistance from court-authorized wiretaps.

Take notes regarding the suspects’ activities, including time, date and location.

Have surveillance team members provide reports of what they observed during the surveillance.

Interview Suspect

Read the suspect the legally required Miranda writes prior to questioning.

Establish a rapport with the suspect, so that a sense of trust can be developed. In many instances, this could help lead to a confession.

Obtain a signed, sworn statement if the suspect confesses.

Write the Report

Document all investigative research performed, evidence obtained along with witness and suspect interviews.

Proofread the report for accuracy prior to submitting it to the prosecuting attorney.

Report the facts of the investigation and do not elaborate or make any conclusions yourself. Don't use conjecture.

Testify in Court

Take the time to reacquaint yourself with the facts of the case prior to trial. Study all of your investigative reports and know the chronological order of events.

Remain calm and don't lose your cool during cross examination on the witness stand.

Listen carefully before you answer any questions and speak slowly. Always answer questions honestly and with sincerity. Make eye contact with members of the jury.


During the investigation, take a methodological approach during every single step and take the time to scrutinize all potential evidence.

According to the Naval Inspector General Investigations Manual, a criminal investigator must remain objective during the investigation in order to seek out the truth.


Always be aware of your safety and never interview suspects alone.

Follow wherever the facts lead you and do not exclude any investigative resource.

Be aware of how to legally obtain evidence without compromising the integrity of the investigation.


Denise Warren has enjoyed writing since 2002. Her articles have appeared in the "Los Angeles Herald" and the "Portland Daily Globe." She also writes health and fitness articles for individual clients and education material for the health care industry. In the hospital setting, Warren has instructed patients on health, diet and fitness programs. She holds a bachelor's degree in nursing from Oklahoma State University.

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