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Traffic collision investigation squad (TCIS)


TCIS Detectives analyzing collision data at a scene.

The Traffic Collision Investigation Squad (TCIS) is a detective unit responsible for scene response and investigative follow-up for collisions involving vehicles, bicycles, pedestrians, boats, trains, light rail vehicles, and aircraft in the following circumstances:

  • The death of any person
  • Injuries serious enough to cause death
  • Hit and run collisions where there is a substantial injury
  • Collisions involving substantial bodily injury where it appears a driver was negligent or under the influence of alcohol and or other drugs
  • Vehicular Homicide
  • Vehicular Assault

TCIS also has follow-up investigation responsibility for all other vehicular crimes, including:

  • Felony Eluding
  • Felony Driving Under the Influence (DUI)
  • Misdemeanor hit and run collisions


At the request of a patrol supervisor and based upon SPD’s callout criteria, TCIS detectives will respond to the scene of serious collisions.  TCIS detectives are subject to callout around the clock.  The on-scene investigative tasks by the TCIS detectives may include locating and documenting scene evidence, taking photographs, mapping the scene with surveying equipment, identifying and analyzing the various types of tire marks and roadway gouges, vehicle inspection, and more. 

These tasks often require that all, or at least a portion of the roadway be shut down to traffic while our investigators do their work in order to protect the evidence and maintain safety for the investigators.  SPD recognizes the inconvenience to the motoring public that roadway closures may cause, and makes every effort to reroute traffic with the assistance of our Traffic Section officers and to reopen the roadway as soon as practical.


After the on-scene investigation is complete, the lead detective is responsible for completing the follow-up investigation.  Investigative tasks may include obtaining search warrants for evidence, interviewing drivers, victims, and witnesses, obtaining medical records, downloading and analyzing the collision-related electronic data from the involved vehicles, analyzing headlight filaments, processing blood evidence, and more.  Many of the TCIS collision investigations require a mathematical reconstruction be performed in order to determine vehicle speed, direction, momentum, etc.  The ultimate goal of a TCIS investigation is to determine the proximate cause of the collision and to hold those responsible for the collision accountable for their actions by forwarding the case to the appropriate prosecuting authority. 


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Headquarters: 610 5th Avenue,
Seattle, WA 98124-4986
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