@kulverstukas - Kommersant article
(original article in Russian - my translation)
Russian investigators still have to find formal grounds for the re-qualification of this case as a criminal case under Art. 205 of the Criminal Code ("Terrorist Act"). Test results from the swabs and scrapings of plane fragments to detect the presence of traces of explosives will at least take a week. Only then do we know if we can talk about a terrorist attack.
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So at this stage it is still a safety investigation and not a formal criminal investigation (with a parallel running, but subordinate safety investigation).