A young Russian shot three of his guests at a party in his apartment in Yekaterinburg in the Urals and then killed himself.
A 17-year-old girl was also hit by the gunfire, but survived with serious injuries, the investigators said.
The apartment owner is also said to have owned the hunting rifle that was found in the apartment and found as a murder weapon.
Why the 34-year-old killed his guests - two men aged 32 and 36 and an 18-year-old - was initially not clear.
At the celebration, drugs and alcohol are said to have been involved, reported the local news portal "Yekaterinburg Online".
The investigation committee in the city about 1,800 kilometers east of Moscow published photos of the crime scene with the traces of blood.
The men and young women are said to have met on the Internet shortly beforehand and then met to celebrate in the 34-year-old's apartment.
Then the owner of the apartment is said to have picked up the gun and shot during the evening.
Icon: The mirror
hej / dpa