BBC Verify has analyzed social media videos and images from Moscow to gain a clearer picture of the explosion that killed Russian Lt. Gen. Igor Kirillov and his assistant.

Ukrainian sources have claimed responsibility for the attack on the commander-in-chief, who has overseen Russian troops’ protection against radiation, chemical and biological agents since 2017. He was sanctioned by Britain in October and accused of being a “major mouthpiece for Kremlin disinformation.”

Lt. Gen. Kirillov was leaving a modern apartment building in southeast Moscow early Tuesday when the device hidden in a parked scooter exploded, Russia’s Investigative Committee – the country’s equivalent of the FBI – said.

Footage confirmed by BBC Verify showed Lieutenant General Kirillov and his assistant leaving the building before the scooter parked next to the main entrance exploded. The clip appears to have been filmed by a camera mounted on the dashboard of a car parked nearby.

Nothing can be seen after the explosion, the rest of the footage is obscured by debris from the explosion.

In other footage analyzed by BBC Verify, the remains of an electric scooter can be seen lying among rubble between two bodies and a destroyed door.

A close-up of the scooter, verified by comparing it with the debris, shows that it is largely intact – except for the missing handlebars.

Experts from Janes – a private open-source investigative organization – told BBC Verify that the images suggested the explosion was caused by an improvised explosive device (IED) and not conventional munitions.

“From the available images of the scooter it actually looks fairly intact, so the effect appears to be more of fragmentation than explosion,” a spokesperson for the organization told BBC Verify.

An IED is a type of “homemade” bomb that can come in a variety of forms and typically contains readily available components such as nails, glass or metal fragments, according to the U.S. Department of Homeland Security.

David Heathcote, intelligence manager at security analyst McKenzie Intelligence, also suggested the device appeared to be an IED.

“IEDs can be deliberately designed to look like an everyday object that doesn’t look out of place,” he told BBC Verify. “In this case, it appears that the device was hidden in a scooter, most likely using a military-grade explosive such as (but not necessarily) Semtex, rather than a homemade explosive.”

He added that the attack “displayed a reasonable level of sophistication and may have taken months of preparation,” which would have required “significant surveillance of the intended target prior to the attack.”

Russian media have speculated that there was a device attached to the scooter’s handlebars.

Citing law enforcement sources, it was also reported that the explosion was likely detonated remotely. Mr Heathcote agreed and suggested a radio signal from a telephone or car fob could have been the trigger.

“The attacker must keep an eye on the device and press a switch to trigger the explosion as soon as the target comes into range,” he told BBC Verify. “The proximity to the attacker’s device depends on the transmitter (or receiver) used.”

Russian state media said up to 300 grams of explosives were used in the bomb. According to a UN explosion damage assessment tool, 300 g of TNT-equivalent explosive can break small windows from a distance of about 17 m (55 feet) or cause damage to brick houses from a distance of 1.3 m.

An eyewitness showed Russian media images of debris from the explosion hitting his apartment across the street from the site. BBC Verify features these weapons experts to find out if they could have come from the device.

According to the developers, the apartment block where Lieutenant General Kirillov was killed is relatively new and was completed in 2019. The apartments are relatively high quality, with some available online for around 20 million rubles (£153,540).

In the videos, verified by the BBC, a small crowd can be seen gathering around the bodies lying on the snow-covered road. Rescue vehicles can also be seen in the footage.

Both videos were filmed on a street looking north toward Ryazansky Prospect in Moscow and surfaced on social media on Tuesday morning. They show damage to the front of the building, including scattered bricks and open doors just meters from the bodies.

In another video, a bright flash can be seen slightly off camera. The force of the explosion sends snow flying from nearby parked cars.

At least ten other apartments on the street were affected by the explosion, the popular Russian Telegram channel Mash reported.

BBC Verify will continue to examine incoming footage from the crime scene and provide updates.