Banner for The Criminal Justice Systems: A Guide for Law Enforcement Officers and Expert Witnesses in Impaired Driving Cases

Law Enforcement Testimony

Standardized Field Sobriety Test Officers1

Standardized Field Sobriety Tests (SFSTs) as promulgated by the International Association of Chiefs of Police (IACP) and the National Highway Traffic Safety Administration (NHTSA) are not generally well known or understood by most jurors. They are, however, routinely used by law enforcement officers in Driving While Impaired (DWI)2  cases, and the arresting officer must be fully prepared to testify in court. Testimonial evidence in DWI cases is usually the only way to establish the fact that the accused was in fact the driver of the vehicle involved in the incident. The officer’s observations may be the only source for establishing that the accused was impaired.

Pre-trial Preparation

Preparation for testimony begins at the time of the incident and requires:   

  1. Recognizing significant evidence and documenting it in the field notes:
    • Observations of or witnesses to vehicle operation
    • Signs and symptoms of impairment
    • Statements by the defendant
  2. Compiling complete and accurate notes
  3. Preparing a complete and accurate report

Preparation for testimony continues prior to trial by:

  1. Reviewing the case file
  2. Discussing the case with other officers who witnessed the arrest or otherwise assisted in it
  3. Mentally organizing the elements of the offense and the evidence that supports it
  4. Mentally organizing the testimony to convey observations clearly and convincingly to the jury and judge

Once an officer receives a subpoena or other notification of a trial date, the officer should:

  1. Obtain and review all records and reports
  2. Revisit the scene if appropriate
  3. Compare notes with assisting officers
  4. Discuss the details of the case and testimony with the prosecutor assigned to the case
  5. Make sure the prosecutor has been given copies of everything required by the law in your jurisdiction prior to trial (which may include handwritten notes, photographs, etc.)


1 Driving While Impaired (DWI) is the term used throughout this publication to refer to driving while under the influence of alcohol and/or drugs. This term is intended to cover Operating Under the Influence, Driving Under the Influence, Driving While Intoxicated, or whatever language is used in your jurisdiction.

2 The authors of this guide would like to thank L.R. “Bob” Jacob of the Institute of Police Technology and Management (IPTM), Jacksonville, Florida for permission to reprint this material from IPTM’s “DUI Case Preparation Manual for the Florida Law Enforcement Officer,” 2001 edition. Any changes, errors or omissions from the original document are the responsibility of the authors of this guide.