The title has a double meaning: First of all, the idea behind it is that of different witnesses (instrument groups) giving testimony about the same event -- the overall picture is roughly the same, while details differ. It's not so much a "theme and variations" thing, though, as just a constantly evolving theme. Which statement presents the "truest" depiction of the event is left to the listener.
Second, while it is not exactly a tribute to him or an attempt to write something in his style (I'm not nearly dramatic enough for that, anyway), the initial flute theme mentioned above did remind me a little of Shostakovich, and so the title of his memoir seemed a fitting name for this, contributing to the "testimony" layout of the piece.
The first four minutes are spent building up to the main idea, the first "testimony", offered by the flutes (twice). It then goes to the clarinets, the bassoons extend it a little, the oboes offer a faster version, and after a percussion/low brass/flute interlude, the trumpets get it, then the horns, and finally the strings (which had participated in the introduction along with the horns, tympani and harp, but hadn't gotten to "testify" yet).
After brief, overlapping statements from the flutes and oboes, the strings get it again, leading into a fugal section based on an "energized" form of the "testimony" idea. From there, well... you just have to listen. At a little more than 16 and a half minutes, for once the music is actually longer than the comments describing it. You're welcome... I think.