Alexei Kovalev, “the deputy head of the military and civil administration in the Kherson region was killed by bullets,” the investigators said on Telegram.
The attack took place in his home on Sunday, they said, adding a young woman who lived with him was also a victim.
They did not give any further details.
In the past months, several Ukrainian officials named by Russian forces in occupied territory have been killed or wounded in attacks.
Kovalev, 33, was elected a deputy in 2019 in Kherson and joined Zelensky’s group in the Ukrainian parliament.
After the Russian offensive on Ukraine at the end of February and the occupation of Kherson by Russian troops, Kovalev joined the invading forces and became a senior official.
He survived an assassination attempt in June.
Russian forces seized Kherson, a town of 280,000 inhabitants, on March 3.
It was the first major city to fall following Moscow’s invasion of Ukraine.