Russia said on Wednesday it had detained a man from Uzbekistan over the killing of a senior Russian general and his assistant in Moscow a day earlier.

Lt. Gen. Igor Kirillov, who headed Russia’s radiological, biological and chemical protection forces, was killed by a remotely detonated bomb planted in an electric scooter outside his apartment building.

The blast came a day after Ukrainian prosecutors indicted Kirillov in absentia for Russia’s use of banned chemical weapons during its invasion of Ukraine. A source with knowledge of the operation later told CNN that Ukraine’s security service, the SBU, was behind the attack.

Russia’s Investigative Committee said the 29-year-old Uzbek suspect was recruited by the SBU and acting on its instructions. It claimed that the suspect had been offered a reward of $100,000 in cash and the chance to flee and live in a European country.

“The detainee received a homemade explosive device and placed it on an electric scooter which he parked at the entrance to the residential building where Igor Kirillov lived,” the committee said.

The suspect had rented a car and fitted it with a surveillance camera to monitor Kirillov’s residence, it added. The footage was monitored by the attack’s organizers in Ukraine’s eastern city of Dnipro, it said, who remotely detonated the bomb when they saw Kirillov and his assistant leave the building on Ryazansky Street early Tuesday morning.