Russia saidit had detained a citizen of Uzbekistan who had confessed to planting and detonating a bomb which killed Lieutenant General Igor Kirillovin Moscow a day earlier on the instructions of Ukraine's security service.
Kirillov, who was chief of Russia's Nuclear, Biological and Chemical Protection Troops, was when a bomb hidden in an electric scooter went off.
He was the most senior Russian military officer to be assassinated inside Russia by Ukraine. Ukraine's SBU intelligence service, which accused Kirillov of being responsible for the use of chemical weapons against Ukrainian troops, something Moscow denies, took responsibility for the killing.
Russia's Investigative Committee, which probes serious crimes, said in a statement on Wednesday that the unnamed suspect had told them he had come to Moscow to carry out an assignment for Ukraine's intelligence services.
"A national of Uzbekistan, born in 1995, was arrested on suspicion of having committed the attack that cost the life of the commander of Russian radiological, chemical and biological defence forces, Igor Kirillov, and his assistant, Ilya Polikarpov", the committee said.
What do we know about the suspect?
In a video of the confession published by the Baza news outlet, which is known to have sources in Russian law enforcement circles, the suspect is seen sitting in a van describing his actions.
Dressed in a winter coat, the suspect is shown saying he had come to Moscow at the orders of Ukraine's intelligence services, bought an electric scooter, and then received an improvised explosive device to carry out the hit months later.
He describes how he had placed the device on the electric scooter which he had parked outside the entrance of the apartment block where Kirillov lived.
Investigators cited him as saying that he had set up a surveillance camera in a hire car nearby and that the organisers of the assassination, who he was cited as saying had been based in the Ukrainian city of Dnipro, had used the camera to watch what was going on.
Igor Kirillov, 54, was the head of the Russian army's chemical, biological and radiological weapons unit. Source: EPA / Sergei Chirikov
He says Ukraine had offered him $100,000 for his role in the murder and residency in a European country.
Investigators said they were identifying other people involved in the hit and the daily Kommersant newspaper reported that one other suspect had been detained.
The blast went off in a residential area in southeast Moscow a day after President Vladimir Putin hailed Russian troop successes in Ukraine.
Kirillov, 54, was recently sanctioned by Britain over the alleged use of chemical weapons in Ukraine.
