Speaking on Tuesday, deputy police chief Unan Pogosyan said that Valeri Permyakov, a soldier stationed at Russia's 102nd military base, located in Armenia, had confessed to the killings.
"Permyakov, the suspect in the murder of six members of the Avetisyan family in Gyumri [Armenia’s second city], admitted his guilt. He said that he left the base in order to walk around the city and happened to be at the Avetisyan's house," Pogosyan told reporters from RIA Novosti.
No motive for the killings has been given.
Pogosyan said that prosecutors from Armenia and Russia are currently negotiating the issue of which party, Russia or Armenia, will conduct the case against Permyakov.
"Russian law enforcement agencies are interested in having the Armenian side lead the investigation," Pogosyan added.
On Monday, six family members including a two-year-old girl were killed with an automatic weapon in Gyumri.
The lone survivor is a six-month-old infant who sustained multiple gunshot wounds and is currently in critical condition in the intensive care unit of Gyumri's children's hospital.
Permyakov came under suspicion after disappearing from the base with his weapon and full combat gear on the same day the murders occurred.
He was arrested by Armenian police and border guards near the Turkish border earlier on Tuesday.