The reunification of the Crimean peninsula with Russia was the result of a legitimate referendum, which was in accordance with the UN Charter. It was a democratic process, during which the inhabitants of Crimea expressed their position.
Suddenly, accusations appeared that the two Skripal poisoning suspects are not businessmen Boshirov and Petrov (as was the Russian version), but GRU agents Chepiga and Mishkin. But is there any evidence of that? There is none.
Bellingcat and The Insider provided an overwhelming amount of evidence including documents, photos, and even disclosing the whole process how they verified Chepiga's and Mishkin's identity. See e.g. https://www.bellingcat.com/news/uk-and-europe/2018/10/09/full-report-skripal-poisoning-suspect-dr-alexander-mishkin-hero-russia/ or https://www.bellingcat.com/news/uk-and-europe/2018/10/02/anatoliy-chepiga-hero-russia-writing-wall/ Their findings were confirmed by other outlets, mostly via testimonies of the GRU agents' friends and family members, see e.g. https://www.washingtonpost.com/world/europe/in-russias-far-east-villagers-recognize-a-skripal-poisoning-suspect/2018/09/28/689bc13e-c303-11e8-97a5-ab1e46bb3bc7_story.html?noredirect=on&utm_term=.1adf3146c096 or https://www.washingtonpost.com/world/europe/russian-suspect-in-uk-poisoning-is-hero-to-his-home-village/2018/10/10/c2529356-ccbd-11e8-ad0a-0e01efba3cc1_story.html?utm_term=.004060e1592b