The government banned people from wearing any form of headgear (eg masks/blalaclavas) during protests. Some protestors have been wearing silly things in their heads as a form of humorous defiance.
https://en.wikipedia.org/wiki/Anti-mask_laws
(Not a commentary on Ukraine; just curiosity).
And especially they wouldn't be: 1. kidnaped; 2. beaten up; 3. found dead somewhere in a forrest, miles out of the city And after that police states - death occurred due freezing, and has nothing to do with kidnaping :)