Killing one man in prison did not decrease political dissent. It was like pushing a beachball under the water. It’s not on top the water where it’s visible, but the force required to keep it submerged will get increasingly difficult to bear. Dissent went from being visible to fleeing the country, to sabotaging the regime where no one can see it. Things as varied as letting the air out of tires on military vehicles to making weapons that fail. It went from one big, noticeable thing to thousands of unnoticeable things that may, over time, add up to regime collapse. This is a game the Russian people have played since about 1905.
There isn't any significant political dissent in Russia. Life has gotten better under Putin for most Russians. The vast majority are behind the war in Ukraine.
The only dissenters are young liberals, the same kind we have in this country that are brainwashed by the same left-wing ideology.