Thursday, November 16, 2006

Collection and use of security video evidence after a crime

The Edmonton Sun has a report on the Michael White murder trial. Mr. White is accused of murdering his wife, Liana, and abandoning her body in her white SUV. City police presented evidence consisting of images recovered from a security video camera at a local pub and an analysis thereof. The images, with their timestamps, show a white SUV being driven down the road where the victim's body was found during the relevant time frame and some minutes later a man of similar build to Mr. White jogging back down the road. None of the images are ID (identification) quality to be sure, but the video was apparently analyzed carefully to see if there was a match with the vehicle and to see if the times and distances were consistent with the prosecution's accusations.

Besides not being widely reported (at least as of now), the other reason I am posting this is to point out how the widespread use of security cameras has caused a change in investigation procedures and workload. Now, after a serious crime has occurred, law enforcement personnel perform a sweep of all security cameras within the area and collect the video on them for analysis.

You might not think it so, but the collection itself can be a major task. In the old days, only a few places generally had them and the ones that did recorded to video cassette. Now, with the advent of hard disk based recorders, just getting the video off the recorder in a way that preserves the original quality is challenging. On top of that, coping with the proprietary codec and playback software is an additional challenge.
Aside: "Codec" is short for coder-decoder, which is the algorithm that translates the raw video into a digital format, which is often of much smaller size and contains significantly less detail.
This brings to mind the July 7th bombings in London, UK. Because the bombings occurred at multiple locations spread across the center of London, thousands of recordings had to be collected and analyzed. This required an incredible amount of effort. In the true spirit of international law enforcement cooperation, a colleague of mine from the USA was detailed to the UK for a year to help out with the work load. You've probably seen some of the images that they found. They not only tied the suspects to the bombing but provided other information as to their methods of operation. So, although the explosion of digital security video camera technology has not been without problems and has also increased the workload substantially, there are significant benefits that has come with it - benefits that may include bringing the correct person to justice for the slaying of Mrs. White.
Note: I would like to make it perfectly clear that I am not making any judgments or claims about the quality or validity of evidence against the accused in this case. As is said in the USA, the "accused is innocent until proven guilty". In any case, evidence may be tossed out, an alibi may be presented, or other events may result in the accused being acquitted, either initially or on appeal.

1 comment:

a.a said...

Aah, a Bayesian blog :)

Yes, both hypotheses could be equally likely.