Monday, April 13, 2015

Dzhokhar Tsarnaev's movement profile after the blasts

Conrad seizes on distance question: "you spent a week on Boylston, took hundreds of photos, don't know distance?" No. 
David Boeri tweet on March 30, 2015

During the questioning of FBI photographer Michelle Gamble defense attorney Miriam Conrad exhibited a keen interest in particulars of the official Forum video whose significance didn't immediately disclose itself to the common observer. (I have documented the cross-examination in my last blog entry.) The distance of Dzhokhar Tsarnaev to the location of the bomb at the moment of the explosion was one of them. Does Conrad have any independent information about the distance that doesn't match the video?

This thought invites to a closer scrutiny of the distance question. It is indeed possible to establish a fairly precise post-blast movement profile for Dzhokhar. I have expounded here that the Forum video and the Fred Land video together cover a big part of the sidewalk, with only a small gap in between. The Forum video shows Dzhokhar walking away swiftly after the first blast (7:43-7:55 in this compilation). When the second blast occurs, he's just at the borderline between Atlantic Fish and Crate&Barrel, almost the same place where he was standing before he went down to the Forum. He then appears in the Fred Land video, now slowly running (8:39-8:45 in the compilation).  

The diagram illustrates the movement profile:

The rhombs indicate Dzhokhar's path, the attached numbers indicate the respective seconds after the first blast. For the first 12 seconds, he's visible in the Forum video. For seconds 22-28, he's visible in the Fred Land video. During seconds 12-22, he's in the "gap".

Thus Dzhokhar's movement profile can conveniently be subdivided into four parts:

1 - Forum, seconds 0-6. He only moves a little bit, looks back, waits, moves again a bit, but doesn't hurry away yet.

2 - Atlantic Fish, seconds 6-12. He hurries away, quickly walking rather than running, with a speed of about 2 meters/sec.

Second explosion occurs.

3 - Crate&Barrel, seconds 12-22. He distinctly slows down, speed about 1,5 meters/sec.

4 - Abe&Louie's, seconds 22-28. He is slowly running now, speed about 2,5 meters/sec.

With the exception of section 3, the speed is simply derived from observing the videos. We don't know what Dzhokhar did in the gap at Crate&Barrel, but most likely he didn't stop for a pause, so I divided this distance into 10 equidistant sections.

This movement profile creates a plausibility problem. Why did Dzhokhar slow down just when the second bomb exploded - one would expect that he would start running like everyone else. But he needed ten entire seconds to bridge the Crate&Barrel gap, which corresponds to a moderate walking, not a running. Something doesn't add up here.

This is even more astonishing as the sidewalk in front of Crate&Barrel is broader than elsewhere, simply because there is no patio there. So the slow down cannot be explained by pedestrian traffic, we would rather expect a speed-up.

At this point, I'd like to recapitulate that there are some peculiar oddities with the Forum video - not matching the Fred Land video is only one of them. Another one is the criminal complaint, which has Dzhokhar not standing behind the tree, but at the barriers, and describes him "calmly but rapidly moving to the west", a calm which is not observable in the Forum video.

It looks therefore legitimate to establish an alternative movement profile, neglecting the Forum video, instead with premises set by the criminal complaint and the Fred Land video:

In this scenario Dzhokhar is standing at the metal barriers between the tree and the mailbox when the first blast occurs. After three seconds, he walks away. When the second blast occurs, he starts running, reaching a speed of 2,5 meters/sec when entering the Crate&Barrel gap and keeping it.

This alternative version looks much more realistic. Here, Dzhokhar must have been in the middle of the Atlantic Fish sidewalk when the second bomb exploded, much closer to the blast than in the Forum video.

Miriam Conrad has of course "insider knowledge" about Dzhokhar's location at the second blast. Is this the only reason she "seized on the distance question" - or is she also aware of footage in conflict with the Forum video?