London ? Russian dissident Alexander Litvinenko likely was poisoned at the bar of a hotel where he met with two other Russians, both of whom are in hospitals showing symptoms of radiation sickness, health investigators said Friday.

For weeks, investigators had zeroed in on a different location, the Piccadilly Circus sushi restaurant where Litvinenko had lunch, believing that was a likely location for his mysterious poisoning with radioactive polonium-210.

But that theory has been shaken by medical evidence showing that seven people who worked at the bar of the Millennium Hotel in London’s tony Mayfair district also have been exposed. The bar has been placed under quarantine.

Police have refused to say where they think the poisoning took place – a crucial question, because it may be the best clue to who did it, and why. One law enforcement official, speaking on condition of anonymity, said detectives have made no final judgment.

But the medical evidence “suggests” that the poisoning likely took place at the bar, Dr. Michael Clarke of Britain’s Health Protection Agency said in an interview Friday.