Addressing reporters on the eve of Georgia's Independence Day, Saakashvili on 25 May described Zhvania's death as a personal loss.
"This year I lost my closest brother-in-arms, a friend, and my most valuable adviser -- such was Zurab Zhvania to me," Saakashvili said. "It was a strong blow to me and a strong blow to the country -- but especially to me. It took me several months to pull myself together, stand firmly on my feet again, and I had no right to show people how difficult it was for me."
Commenting on the televised press conference the following day, Georgian media noted the president had failed to address the many questions that keep swirling around the official probe into Zhvania's death.
Opposition leaders, independent legal experts, and journalists, family members, and friends of the late prime minister have from the onset raised doubts about the official version given by the government.
The haste with which authorities concluded that the two men died of poisoning -- even before the forensic examination had started -- and the contradictory official statements regarding the volume of carbon monoxide contained in their bodies aroused particular suspicion.
Elene Tevdoradze, a member of the Georgian parliament's majority, indicated as early as 9 February that she and other close friends of the late prime minister had doubts that the men died as the result of an accident.
The following day, on 10 February, Davit Gamkrelidze, the leader of the minority opposition in parliament, demanded that the legislature conduct its own investigation into Zurab Zhvania's death.
"We must tell the public -- not only our own citizens, but also the entire world -- whether this was a tragic accident, or a cruel contract killing, and what the government is planning to do about this," Gamkrelidze said.
The largely pro-government parliament, however, did not follow suit.
Since February, Zurab Zhvania's younger brother, Goga (Giorgi), has been conducting his own investigation with the help of friends, relatives, and Yusupov's family. He told RFE/RL he believes the official probe is flawed.
"I've been collecting information [on the circumstances surrounding my brother's death] for several months now and this information is arousing serious queries with regard to this [official] version," Goga Zhvania said.
Goga Zhvania has demanded that an independent probe -- possibly involving European experts -- be conducted into his brother's death. He said he will officially press Saakashvili to authorize such an investigation when he meets with him on 28 May.
Asked whether he thinks his brother was assassinated, Goga Zhvania said: "Before I only had suspicions. Now, I'm almost sure he was. Zurab had many, many enemies."
Zurab Zhvania's widow, Nino Kadagidze, said she shares her brother-in-law's concerns regarding the official probe.
In comments broadcast on television on 25 May, Kadagidze charged that Georgian authorities were "doing their utmost to substantiate the accident theory" while neglecting all other possible versions.
"The investigators must either admit this was not an accident, or produce evidence showing this was an accident," Kadagidze said. "There is no other alternative."
Government officials have repeatedly dismissed the assassination theory. Saakashvili spokesman Gela Charkviani on 4 April said there was no doubt that Zurab Zhvania's death was accidental.
"When professionals say something, one ought to trust them," Charkviani said. "In the present case, we're talking about two groups of professionals -- one made up of Georgians professionals who investigated this case, and one made up of FBI agents whose conclusions coincide [with those of the Georgian investigators]."
Upon a request made by Georgian authorities, a group of FBI officers arrived in Tbilisi on 8 February to help investigate Zurab Zhvania's death.
Three days later, Bryan Paarmann, the legal attache of the U.S. Embassy in Georgia, announced that the American experts had found no evidence that would contradict the initial conclusions of their Georgian colleagues and that there was "no reason to allege that a third party was involved in the incident."
Yet, Goga Zhvania maintains that the FBI conclusions were in fact quite different.
"The FBI investigators conducted an experiment in the apartment [where Zurab and Raul were found dead] and examined the organs of the deceased," Goga Zhvania said. "Forensic examination had shown carbon monoxide had spread into the bodies of the deceased, causing death by poisoning. [The U.S. team] tested the apartment's gas heater. Officially, the carbon monoxide found in the bodies of the two deceased had leaked out from this gas heater. But the tests made by the U.S. investigators show the heater was functioning ideally and that there had obviously been no carbon-monoxide leak [in the apartment]."
Goga Zhvania said his assertions are based on a copy of the FBI report he obtained from the Prosecutor-General's Office. He also said the U.S. document and the official Georgian translation differ widely and sometimes even contradict each other.
Attempts to obtain a copy of the report from the FBI produced no immediate results. An agency spokeswoman in Washington told RFE/RL that no information could be provided regarding the document until a Freedom of Information Act request is filed.
Goga Zhvania cited what he says are other "troubling facts" regarding the official probe. For example, he said, no fingerprints of the deceased were found in the apartment where the prime minister's bodyguards reportedly found the bodies shortly after 4:00 a.m. He also pointed to another detail.
"No cigarette butts that could have been left by Zurab were found [in the apartment]," Gogi Zhvania said. "He had a peculiar way of stubbing out his cigarettes. Also, the testimonies given by his bodyguards are extremely dubious. Sometimes they contradict each other, sometimes they lead to a dead end."
Kadagidze on 25 May also cited discrepancies she noted in the testimonies of Zurab Zhvania's bodyguards.
She also alleged that the head of her late husband's security team spirited away keys from the prime minister's dead body and rushed to the State Chancellery. She claimed many documents were later found missing from his safe.
Goga Zhvania said that so far there have been no attempts to prevent him from investigating his brother's death. However, he complained of what he described as "psychological pressure."
"There have been no threats per se. But some people told me that should I continue to dig for clues, I would regret it," Goga Zhvania said.