A knife-wielding man went on a stabbing rampage in the Russian city of Surgut on August 19, wounding seven people before he was shot dead by police, investigators say.
The extremist group Islamic State (IS) claimed the attacker was one of its militants, according to the IS-affiliated Aamaq news agency.
The Investigative Committee described the suspect as a local resident born in 1994, and said that investigators were looking into "his possible psychiatric disorders."
The statement gave the number of victims at seven, down from an earlier tally of eight.
Investigators opened a criminal probe into attempted murder.
Interfax news agency quoted the regional Interior Ministry as saying that authorities did not suspect terrorism as the likely motive.
Regional officials said four of the wounded remained in a serious condition.
Surgut is the center of Siberia's oil industry. The city has 300,000 residents and is located some 2,100 kilometers northeast of Moscow.
The IS group also claimed responsibility for attacks in Spain on August 17 that left 14 people dead.