Ukraine's security service on Wednesday said it had identified two suspected informers who allegedly helped Russia strike at a wake last week, killing over 50 people.
The SBU named two local men now living in Russia, saying they were suspected of giving information that led to a missile attack on the village of Groza in the Kharkiv region, one of the deadliest strikes of the war.
On October 5 a missile hit a large gathering at a cafe for the wake of a Ukrainian soldier, killing 55.
The SBU said the suspects handed over details knowing that local civilians would "surely die" in an attack.
The SBU named the suspects as 30-year-old Volodymyr Mamon and his 23-year-old brother Dmytro Mamon, who have both fled to Russia.
Dmytro was a traffic policeman, while Volodymyr was a police escort driver under the occupying authorities, according to documents posted by the SBU.
Parts of Kharkiv region were occupied from February to September 2022.
The security service posted phone messages from Volodymyr Mamon asking about the wake's location and the dead man's military service.
"Having learned the exact address and time of the peaceful event, Volodymyr Mamon gave this information to the Russian occupiers," it said.
"The Russians used the information received to carry out a targeted attack on the Ukrainian village using the Iskander-M operational-tactical missile complex."
After moving to Russia, the brothers had continued communicating with a "network of informants" in Ukraine-controlled territory, the security service said.
They asked about troop deployments and mass events "under the guise of friendly conversations".
The two men are suspected of jointly plotting high treason and deliberately collaborating with an aggressor state.
Volodymyr Mamon is also suspected of committing a war crime with the intention of murder.
A spokesman said the SBU was attempting to locate the men and bring them to justice.
An investigation by Radio FreeEurope/Radio Liberty last year reported that Volodymyr Mamon drove a car with the pro-Russian "Z" sign during the occupation, delivered provisions to Russian soldiers at checkpoints, looted and searched for Ukrainian soldiers.
He is currently on trial in absentia in a court in Poltava for high treason.