and in my opinion Britain might have done it themselves just to gain grounds for intervention in Russian policies, they wanted us to change our Constitution.
He knows our master plan!
*Agent Mongoose will now terminate TheGreatEmperor*
Truly, this is one of many conspiracy theories surrounding it.
It was a terrorist plot to destabalise relations between the US, UK, and Russia and start World War III
The same story as above, except replace the terrorists with FSB, MIB and New World Order
It was a rogue American/British Intelligence cell still fighting the cold war (!)
The spy actually killed himself to prevent his secrets being learned by MI5 and the CIA, since he had knowledge of some new Russian superweapon
This is just a sample, as you can see they go from plausible to downright crazy...