Random thought, but if it was a truck bomb (challenging, but not impossible, due to the security scanning systems the Russians have in place), was it a suicide bomb, or did the Ukrainians (or CIA, or James Bond, or whoever) somehow sneak a bomb onto a Russian truck, and then trigger it while it was one the bridge (timer, GPS, the GWOT classic cell phone detonator, heck maybe even a link to the truck's odometer, I don't know).
Suicide bombs are almost unheard of outside of jihadi circles, and I haven't heard of the Ukrainians employing them at all.