The witness letter from Sidlo implies some involvement in the incident. Roughly translated it says
"I attended the races in question, but also in the unfortunate round. I drove a 4-you completely on the right side. On the left of me riding Pole. When I turned in the south wiraz, felt the impact of the rear near my machine. I let the machine immediately crashed to the ground. Wlecialem by up to forward the grating, which in the south-vertex wirazu envision, namely com clock for football matches. My-deprived driver's machine went on and fell under the stairs, which have there, there were the but, in any case not reached until the racetrack. I found myself in the grating at a distance of approximately 4m from the stairs. Pole went to his machine on and it fell into the place where my machine was lying. this is the place popup about 3m. It is separated from the outer edge of race track and so is the up outside.
Straw bag was at the beginning of the bars mentioned by me, but not when or under critical concrete stairs. by polak tem away before he met with a ride-on 2 Nd Biskop position, that he could not tell, because I have not noticed. in question was running races for the rest of Austria. After the break race for intensified in August, as I recall-before the present unfortunate accident were to place two further cases, however, without mortal consequences.
or Pole already by collision with me injured, I do not know. Pole certainly went full throttle, the Pole did not want in asc but was on his machine".
I've also roughly translated Kamper's witness statement and that also implies Sidlo was involved in the accident. It looks to me like Sidlo had replaced Seidl in the race and was involved in the crash.