Russia’s National Anti-Terrorism Committee reported that the cause of the explosion on the bridge was "the explosion of a truck, which led to the ignition of seven fuel tanks of the [nearby] train." The truck that allegedly exploded on the bridge at around 6 a.m. Saturday morning underwent inspection in Taman before making its way onto the bridge. From surveillance footage, officers can be seen asking the driver of the car to open the cargo compartment of the van. After a quick check, the truck drives on to the bridge and, a few minutes later, explodes. At the entrance to the Crimean bridge, special X-ray equipment has been installed, which ought to pick up explosives in vehicles. But on this particular occasion, the Mash telegram channel reports, the truck was not checked by these methods. Another Russian Telegram channel, citing a source in law enforcement agencies, wrote that the traffic officers who checked the truck had been “detained and interrogated.” The driver may have been fully aware that it would be his last trip. “The main issue is the human factor: It's either bribe or negligence,” they write, noting that “a convenient time had been chosen for the explosion [early Saturday morning] when all the smugglers go to the peninsula.”
The Telegram channel also pointed out that “the employees participating in inspections can earn an extra million rubles a day [$16,000],” by turning a blind eye to the loading of trucks and the transport of prohibited goods. BellingCat Investigator Khristo Grozev on Twitter, attempted to answer the question of how the amount of explosives needed to destroy several spans of the bridge could have made its way on to the bridge undetected. He suggested that something "legal" but "weaponizable" could have been used, such as ammonium nitrate, which is also used as a fertilizer.