Search continues in the Tula region. The plane fell from a height of five to six kilometres on a swampy terrain, he explained.
The scrutiny revealed traces of hexagon in the explosion fragments, the general said. They were not found in the first examination of the Tu-134 wreckage.
After the fragments had been retrieved from the swamp, FSB experts examined the cabin on August 27.
"They found typical damages from the blast wave on passenger seats and tables", Fetisov said. Samples were taken to Moscow for study.
"Expert examination provided us with trustworthy information on August 27 that an explosion containing hexagon happened also in that plane", the general said.
On August 24 two passenger jetliners - Tu-134 and Tu-154 - crashed in the Tula and Rostov regions, killing 90.
Results of a criminal examination become a fact only if they are 100-percent trustworthy, he noted. "They become a legal fact when undersigned by an expert, who bears legal responsibility", Fetisov added.
From the very beginning, investigation considered four versions, one being on-board explosion. "Only when trustworthy results of the examination appeared, an explosion could be spoken of", he said.
Fragmentation damage has not been discovered.
"The fragments are being laid out to complete the technical examination. No fragmentation damage was found in superficial inspection", the general said.
