If a VIP is hanged then he stays hanged. Any assassin can carry a few feet of sturdy synthetic rope, or know where one can be obtained. On the other hand, a suicidal man can hang himself on a weak support, with a flimsy rope - and fall on the floor, dead, after the support, or the rope, fails.
It is reported that he was found inside a locked bathroom. Most bathroom locks do not have a key and cannot be locked from the outside. That particular door was broken by the security guard; he wouldn't have to do that if he had a key. Such a lock does not permit an assassin to exit the bathroom and lock the door behind him. Therefore, nobody exited the bathroom.
It is far more realistic to conclude that Berezovsky was destroyed financially, politically and morally - because all that has actually happened and was in the news for everyone to see. He lost a major lawsuit and owed hundreds of millions. He lost his house in London and was living in a faraway house of his ex-wife. He lost all his entourage; he had only one guard (more like an assistant) left by the day he died. Suicide is likely because he had no way to get out of this situation. He even spoke of suicide with some of his friends.
The detective may be unwilling to deny a possibility of murder, but I think that's just because the police is not in a hurry to commit to this or that scenario. Why should they? Who benefits from a speedy conclusion? Nobody. So the police will do it all by the book, with all proper lab tests and with whatever else they are supposed to do.
Did the bathroom have a window? How many floors was it above the ground? What about the death of the high profile French lawyer also reported here at FR?
The continuation of the article says there was no suicide note, and it happened in his $20 million mansion. How much did he owe on the mansion? Was he broke or not?
Many of these 'privacy' lock sets can be locked upon exiting the room by simply pushing a button or turning a knob (depending on the lock-set) to 'lock' on the inside and pulling the door shut when exiting.