Why and when is audio-video evidence used?
In the movie, The Fugitive, Dr. Richard Kimble, played by Harrison Ford, is on the run from police. He calls the Chicago Police Department to proclaim his innocence. He ends the phone call before it can be traced, but there was one thing he didn’t anticipate—the sound of the L train can be heard in the background. By analyzing the recording, the police know he’s calling from Chicago.
While most audio evidence won’t launch a city-wide manhunt, it may aid the investigators in piecing together the facts of a case. Audio from a recorded 911 phone call, for instance, can provide key information—not only from the words of the caller, but from sounds in the background. Can the assailant be heard in the distance? How many parties are audible on the tape?
To Corroborate Statements
In many cases, audio and video evidence can be used to corroborate subject or witness statements. For instance, video from a security camera can provide information on the direction or means of travel into or away from the crime scene. Did the subject flee in a 4-door, red Ford? Did he depart the scene heading north or south? The recorded footage can confirm a witness statement.
Sometimes a video surveillance camera is the only eyewitness to a crime. Video evidence was key in finding and identifying the perpetrator in the abduction and killing of 11-year-old Carlie Brucia of Sarasota, FL. Video from security cameras showed her being taken from a carwash parking lot and led away by a middle-aged man wearing a work uniform. The video of the abduction circulated nationwide on television and a housemate of the perpetrator called police when she saw the footage.
Upon enhancement of the video recording, investigators were able to provide clearer images of the man’s face, tattoos on his forearms, and even the name tag on his uniform.
To Identify Suspects
The power of video evidence in aiding an investigation is illustrated by a website created by the Vancouver Police2 to identify suspects from the infamous 2011 Stanley Cup riots. After painstakingly reviewing the video evidence, photos of rioters have been extracted from these videos and posted on the site for identification by the general public.
Even if video or audio evidence does not capture key actions of the crime, the recording may be able to add information or provide additional details such as the appearance of the perpetrator or what they were wearing.
Vancouver Police Department, Integrated Riot Investigation Team, Vancouver Riot 2011: Help Identify Suspects