British authorities announced Wednesday that they are officially treating the fatal poisoning of former Russian spy Alexander Litvinenko as murder and have found traces of a radioactive substance at the British Embassy in Moscow.

Scotland Yard had been calling Litvinenko’s poisoning “a suspicious death.” Failure to immediately call his Nov. 23 death a homicide had fueled speculation that he might have committed suicide; family and friends, upset over that suggestion, said no one would choose such a frightening, agonizing death.

“It is important to stress that we have reached no conclusions as to the means employed, the motive or the identity of those who might be responsible for Mr. Litvinenko’s death,” British police said in a statement.

In Moscow, British detectives found small traces of a radioactive substance at the British Embassy, but said it posed no risk to public health. They offered no explanation for the radiation, but the embassy was where officials had recently questioned Andrei Lugovoy, a former KGB agent who met with Litvinenko in London on Nov. 1, the day he fell ill.

Lugovoy is in a Moscow hospital undergoing tests and is expected to talk to British investigators Thursday, according to Russian news reports. His attorney, Andrei Romashov, told reporters that his client would be questioned as a witness, not a suspect.

The Interfax news agency quoted Lugovoy as saying: “As for the hullabaloo about me that has been stirred by Western media, in my view good theatrical directing is traceable here. I’ve stopped watching television and reading papers. I’m fed up with all this.”

A Russian police car is parked near the gates of the British Embassy in Moscow. British investigators on Wednesday declared the poisoning death of for KGB spy Alexander Litvinenko a murder.

Dmitry Kovtun, a Russian businessmen who also met Litvinenko on Nov. 1, was questioned Wednesday by investigators from the Russian prosecutor general’s office with detectives from Scotland Yard present. There has been tension between London and Moscow over strict controls Russia has imposed on the visitors’ rights of inquiry.

So far, only two other people have been found to have polonium-210, the radioactive substance that killed Litvinenko, in their systems: Litvinenko’s widow Marina and Mario Scaramella, an Italian who also met with Litvinenko Nov. 1 in London.

Doctors said Marina Litvinenko has such a tiny amount that her risk was low, but more significant quantities were found in Scaramella. But health officials, while concerned for Scaramella’s long-term health, said he was not showing any symptoms and discharged him Wednesday from a London hospital.