British officials say police have cracked the murder-by-poison case of former spy Alexander Litvinenko, including the discovery of a "hot" teapot at London’s Millennium Hotel with an off-the-charts reading for Polonium-210, the radioactive material used in the killing. Click here for slideshow of the Litvinenko investigation. A senior official tells ABC News the "hot" teapot remained in use at the hotel for several weeks after Litvinenko’s death before being tested in the second week of December. The official said investigators were embarrassed at the oversight. The official says investigators have concluded, based on forensic evidence and intelligence reports, that the murder was a "state-sponsored" assassination orchestrated by Russian security services. THE BLOTTER RECOMMENDS Photos Murder in a Teapot: The Investigation Into Litvinenko’s Murder Blotter $1 Million Hit? The Real Deal on Polonium Click Here to Watch the Latest Brian Ross Webcast. Officials say Russian FSB intelligence considered the murder to have been badly bungled because it took more than one attempt to administer the poison. The Russian officials did not expect the source of the poisoning to be discovered, according to intelligence reports. Russian officials continue to deny any involvement in the murder and have said they would deny any extradition requests for suspects in the case. Click Here for Full Blotter Coverage. Sources say police intend to seek charges against a former Russian spy, Andrei Lugovoi, who met with Litvinenko on Nov. 1, the day officials believe the lethal dose was administered in the Millennium Hotel teapot. Lugovoi steadfastly denied any involvement in the murder at a Moscow news conference and at a session with Scotland Yard detectives. Russian security police were present when the British questioned Lugovoi, and British officials do not think they received honest answers from him. British health officials say some 128 people were discovered to have had "probable contact" with Polonium-210, including at least eight hotel staff members and one guest. None of these individuals has yet displayed symptoms of radiation poisoning, and only 13 individuals of the 128 tested at a level for which there is any known long-term health concern, officials said. The Millennium Hotel has closed the Pine Bar and other areas where Litvinenko and Lugovoi met on Nov. 1, although the hotel says the remaining public areas "have been officially declared safe" and are open to the public. Read the"Response to Press Speculation" released by Millennium & Copthorne Hotels.