Deniable assets may have performed the computer attacks and assassinations. The real deal is flying several stealth aircrafts armed with guided air-to-ground munitions over Europe, leaving no trace. It's not like stealth bombers are a widespread commodity.
Core books, London Source, Germany Sourcebook and Shadows of Europe gives little information. The odd part is, Great Britain does not appear to really stand out among the suspects like it should. Maybe the Brit provided some conclusive evidences, somehow challenging the aircrafts identification as Nightwraith. Still, according to the London Sourcebook, diplomatic relations between France and Great Britain became glacial from that point.
What amazes me the most in this whole story is someone had the guts to fly the planes in the first place. Right before the attack, Great Britain sent troops to the low countries to protect its interests, thus openly admitting they were threatened. Then someone had bombers that could pass for British models, coming from the North Sea and the general direction of the British Isles, and heading east. Had the Russians detected the planes, instead of the Swedes, this would have been the perfect trigger for a nuclear conflict.
It may worth noting US Air Force Major David Gavilan and corporate spook Lucien Cross were in Stockholm to launch the Nanosecond Buyout, on January 24th, the following day the Swedish air defense detected the aircrafts.
