Jul 17, 2014

Second week of July: Forensic expert analysis of crater

The first witness of this week to give evidence for the Prosecution was Bart Hoogeboom, an expert in image analysis (photogrammetry) from the Dutch Forensic Institute. This expert witness analysed photographs of the crater and its surrounding in order to determine the size of the crater. His results have been put in an expert report tendered by the Prosecution.

[Screenshot of witness Bart Hoogeboom]

Hoogeboom made a selection out of photographs originating from the press, and this resulted in three distinctive sets of photos to be used for his research: one set of photos of the crater taken shortly after the explosion and two sets of photos taken four days after the explosion, totalling 13 photos. Further, he had at his disposal data resulting from a laser scan done by the Dutch police in 2010 at the site of the bombing, providing a 3D representation of the surroundings of the crater (the crater itself had already been closed at that time).

After expert Hoogeboom had made a photo selection, he extracted 3D information from these photos in order to determine the dimensions of the crater. With the first set of photos he was able to identify a number of points in the crater. He combined this information with the other two sets of photos, showing views of the buildings together with the crater, in order to obtain a scale. With the use of special software he calculated the position of the cameras that had been used to take the photos, which was needed to determine the true location of certain points. He subsequently combined the 3D information obtained from the photos - by using corresponding points between the sets of photos – and the data from the laser scan.

[screenshot of a page of Hoogeboom’s report showing corresponding points between photos]

This  technical exercise led to the determination of a numbers of points near the edge of the crater. The actual measurement of the crater was done by fitting a mathematical shape, a partial cone, in the crater. On the basis of this conical shape, the dimensions of the crater could be calculated: 11.4m for the diameter for the top circle of the crater, a 8.3m diameter for the lowest circle, and a height of 1.9m (although the witness admitted that there were definitely lower points in the crater). Of course, there is also a margin of appreciation in this measurement because of the difficult shape of the crater, but the witness stated that the margin of error is expected to be less than a few percent.

The evidence given by this witness was thus of a very technical (and mathematical) nature and seems uncontested by the Defence, as the witness was not cross-examined by any of the teams.

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