http://rt.com/news/gagarin-death-truth-revealed-674/
With the aid of computers, the fresh investigation was able to glean insight into exactly what caused Gagarin to go into a fatal spiral at breakneck speed. They did this by inputting Gagarin’s 55 second plunge together with the 750km speed at which he crashed.
“So we used a computer to figure out a trajectory that would relate to this interval of 55 seconds. And it turned out to be a deep spiral. Now, a jet can sink into a deep spiral if a larger, heavier aircraft passes by too close and flips it over with its backwash. And that is exactly what happened to Gagarin. That trajectory was the only one that corresponded with all our input parameters.”