Keep in mind this can also be used as hero theatre which happened in the orange revolution if I remember correctly, also an alleged poisoning and still, 15 years later, very murky. Both sides can lie.
As per John Le Carré's Moscow rules: 1. Assume nothing.
Except official state propaganda release such interview with their own spy agency staff to prove their innocence. Waning: too funny, you might die of laugh:
Orange revolution happened 14 years earlier [1].
One of candidates in presidential campaign was pro-Russian, and other -- wasn't. There was an attempt to poison to death the later one [2] with a toxin that's part for Agent Orange, there is some irony in that, because Yuhscheko's party had orange colors.
As per John Le Carré's Moscow rules: 1. Assume nothing.