It should therefore be in the interest of the prosecution to handle this crucial piece in an open way to avoid any smell of secrecy. In fairness to Tsarnaev, whose life the prosecution wants to take away, the video should be available to the public in unredacted form, from a few minutes before the blast to a few minutes after the blast.
Unfortunately, this hasn't happened. The video was kept hidden from the public until the begin of the trial. The first clip was shown to the jury on March 4th, 2015, the second day of testimonies. It was available to the public a little bit later (Source). But this version of the video covers only the time before the blast and ends half a second after; the aftermath was at that time only documented by a few stills.
The jury had to wait until April 6th to see a continous version of the video, with pre-blast footage, the blast itself, and a few seconds of the aftermath without any cut. This was at least the perception of some observers. They were apparently wrong.
According to jane24, who is a regular attendant of the trial since the pre-trial phase and whose accurate reports fixate many details which would have gone by the board otherwise (the longest sidebar in history), the clip was probably not uncut. jane24 vouches for having noticed a discrepancy in the clip: before the blast, about fifteen people were on the Forum's patio in the foreground, cheering the runners. After the flash of the explosion had settled and the screen cleared, the patio was emptied: all the people had suddenly vanished.
Here is a snapshot, taken fractions of a second before the blast:
|Forum video immediately before the blast
The people on the patio certainly needed a few seconds to flee the location. And in the very last frames of the available online Forum video (not in the video shown at court on April 6th!) there are indeed the outlines of some people visible after the flash:
|Forum video immediately after the blast
In the video clip shown to the jury on April 6th, jane24 claims, there are no people on the patio anymore. Conclusio: the video re-starts about 10-20 seconds after the blast, after people have left the patio, and the missing seconds have been cut out. In other words: the government keeps withholding crucial evidence from jury and public for whatever reason.
10 seconds removed, is this really a big deal? Yes it is, because as I have argued here, the very first seconds after an explosion are most important for determining its epicenter by comparing the pre-blast and post-blast location of people. A 10-second gap makes this determination much more complicated because people might have moved and changed their location meanwhile.
But maybe the aggravated determination of the epicenter is exactly what the government intended to achieve by cutting off the 10 seconds.