CNN  — 

The huge explosion on the Crimea bridge shortly before dawn on Saturday severely curtailed road and rail traffic along an important artery – both civilian and military – at a critical moment in Russia’s campaign in Ukraine.

At first sight, it was another embarrassment – even humiliation – for the Russian state, still reeling from battlefield setbacks in Kharkiv, Donetsk and, more recently, in Kherson in the south.

But by Monday the bridge attack had also become the Kremlin’s justification for a sudden blitz of missile attacks across Ukraine. By midday, according to Ukrainian authorities, some 80 missiles and rockets had been fired at infrastructure in a dozen cities – and Russian officials were promising more to come.

In the hours after the bridge explosion, Russian investigators fastened onto one explanation for the blast: It was a terrorist attack using a massive explosive charge hidden in a truck and then detonated as the vehicle crossed the bridge toward Crimea.

Russian President Vladimir Putin picked up the theme on Monday, saying Kyiv had “put itself on a par with the most odious terrorist groups,” which had prompted the subsequent “massive strike with precision-guided weapons on Ukrainian infrastructure – energy infrastructure, military command and communications.”

Cars burn after a Russian military strike in central Kyiv on October 10.

“It is simply impossible to leave the crimes of the Kyiv regime unanswered,” he said.

Putin went on: “In terms of the further act of terrorism on the territory of Russia, the Russian reply will be harsh and will be corresponding to the level of threat to the Russian Federation, have no doubt about it.”

A flurry of theories

The explosion, Moscow’s version of what happened and the absence of any Ukrainian acknowledgement for carrying it out, has set off a firestorm of theorizing about what caused it and who was responsible.

The Kerch bridge is about 150 miles from the nearest Ukrainian positions, and well beyond the range of weapons provided by the West. But Ukrainian drones were reported to have approached the area in the summer, setting off air defense measures.

Some analysts unconvinced by the truck bomb narrative suggested a missile or missiles fired by drones may have been responsible, or that an underwater sabotage team had fixed charges to the bridge’s support structure.

Images and video from the scene were inconclusive. As the truck identified by the Russians crosses the bridge and begins to ascend to its highest point, it is engulfed in a massive explosion.

The Russian Investigative Committee, charged with finding out what caused the explosion, quickly identified the vehicle. Surveillance video emerged of the truck, with its distinct scarlet cab, at a checkpoint before it enters the bridge. It receives a cursory inspection; the driver – in a short-sleeve shirt – is seen briefly closing the truck’s rear doors.

But it’s unclear how a truck bomb would have caused two separate spans of the westbound lanes to collapse into the Kerch Strait. Additionally, the force of such a blast would have mostly gone upwards and outwards. Some analysts note that the way the spans collapsed imply the force of the blast came from below.

Chris Cobb-Smith, an analyst with the research group Forensic Architecture, is skeptical about the truck narrative. “It’s possible to blow a bridge by using explosives on the span but it takes a huge amount and needs ‘tamping’ – a huge weight of ballast on the charge to ensure the blast goes downwards,” he told CNN.

A fire broke out after the huge blast on Saturday at the Kerch bridge. The crossing links the Crimea peninsula to the Russian mainland.

“I don’t believe a truck bomb could have caused this level of damage. This would have entailed a suicide bomber driver, unheard of in the context of this conflict.”

Cobb-Smith, a British army veteran, is also skeptical of a special forces operation. “There are accurate weapon systems that could achieve the aim of destroying the bridge without risking individuals.”

But he cautions: “To solve this I believe we need analysis of the bits of the bridge currently underwater. I still think this would have been easily achieved by a precision munition.”

On Sunday, the head of Russia’s Investigative Committee, Alexander Bastrykin, doubled down on the truck explanation.

Face-to-face with Putin in a well-choreographed exchange, Bastrykin said the truck had been in Bulgaria before traveling through Georgia, Armenia, North Ossetia and into Russia. (It would have also had to cross Turkey.)

“It was possible to identify suspects from among those who could prepare a terrorist attack, and people who operate on the territory of the Russian Federation,” Bastrykin said, referring to “citizens of foreign countries who helped prepare for this terrorist attack.”

The investigators reached an “unequivocal conclusion – this is a terrorist attack that was being prepared by the Ukrainian special services,” Bastrykin said.

A stern-faced Putin responded: “I see.” Notably, the president went on to say: “There is no doubt that this is a terrorist attack aimed at destroying the critical civilian infrastructure of the Russian Federation,” carried out by the special services of Ukraine.

On one level, the “act of terror” narrative would at least excuse the Russian military from having to explain why its multi-layered defenses around the bridge failed, despite Ukraine’s public assertions that it was a legitimate target. On another, it provides – through Moscow’s prism – the justification for the massive escalation of attacks on Ukrainian infrastructure.

Ukrainian intelligence claims those attacks were planned days before the Kerch explosion. Its defense intelligence agency said Monday that Russian military units had “received instructions from the Kremlin to prepare massive missile strikes on the civilian infrastructure of Ukraine on October 2 and 3.”

Local residents examine a crater following a missile strike in Dnipro on Monday.

An obvious target

If it wasn’t the truck, what might have caused such an explosion? Cobb-Smith says a surface vessel of any sort should and would have been detected.

Some analysts have suggested that the explosion could have come from beneath the bridge; others think satellite images indicate the impact was from above and came from the north.

Ultimately, according to Cobb-Smith and other experts, there is insufficient video evidence to confirm what happened at Kerch.

There is no doubt that the Ukrainians have seen Kerch as a legitimate, even necessary, target.

Back in June Dmytro Marchenko, a Ukrainian Maj. Gen. Major General in the south of the country, said the Kerch bridge was the “number one target.”

Marchenko told Radio Liberty: “This is no secret to their military or our military. Neither for their civilians nor for our civilians. This will be the number one target to hit. It’s as if the main gut tightening reserves just have to be cut off. As soon as this intestine is cut off, they will begin to panic.”

But Ukrainian officials have been tight-lipped about Saturday’s explosion, welcoming the crippling of the bridge (somewhat prematurely given that limited road and rail traffic resumed within 24 hours) without acknowledging involvement.

They took the same approach with the sinking of the Russian battleship Moskva. It was weeks before any official acknowledgement emerged.

Some Ukrainian officials put the Kerch explosion down to an internal power struggle between Russia’s Security Service and Defense Ministry, without offering any evidence.

Mykhailo Podolyak, an adviser to President Zelensky’s chief of staff, said Saturday that “the logistics of the detonation, the synchronization with the fuel echelon [the rail wagons carrying fuel], the volume of the destroyed road surface - all this clearly points to the Russian trail.”

The cause of the Kerch blast, and its perpetrator, remain open questions. They may do for some time to come. But there is no doubt that the conflict in Ukraine has moved to yet another level, with Russia now embarked on a relentless assault against Ukraine’s power and communications networks, and Ukrainian officials swearing revenge for every missile.