For the past 20 days, a mysterious explosion in the White Sea area of Northern Russia that left five nuclear scientists dead has been the focus of worldwide speculation. While Russia has acknowledged that it was a weapons test gone wrong, it has been coy about the radioactive elements involved in the accident. Western analysts have suggested Russia may have been testing a missile powered by a small nuclear reactor, but sketchy statements from Moscow draw a picture of a different sort of radioactive device.

The city of Severodvinsk, near where the accident occurred, reported a spike in radiation levels in the immediate aftermath of the blast. That report was censored, but soon after, Rosatom, Russia’s nuclear agency admitted that the accident had involved an “isotope power source.”

But data released Monday by Russia’s weather service, Rosgidromet, suggests otherwise. Certain radioactive isotopes the agency measured in the wake of the blast could only have come from an accident with a nuclear reactor, and not an isotope power source, numerous experts say.

The contradictory reports from Russian officials, and the near daily revelations in the media of newer information about the blast, suggest that we have yet to hear the full tale of what happened that day. Here are the highlights of what we know so far:

On Thursday, August 8^th, the Russian Defense Ministry reports an explosion at the Nyonoksa missile test site along Russia’s Arctic coast in the Arkhangelsk region. The ministry releases a statement saying “there was an explosion and fire during a test of a liquid propellant jet engine,” adding that two had died. Later the same day, Kseniya Yudina, a spokeswoman for the city of Severodvinsk tells the official Tass newswire that a “brief rise of the radiation level was registered in Severodvinsk at about noon.”

The Defense Ministry’s statement, however, contradicts that and says, “the radiation background is normal.” Yudina’s statement is subsequently removed from Severodvinsk’s official website.

In the meantime, social media sleuths post pictures of workers wearing hazmat suits as they transport victims of the blast from ambulances to helicopters, suggesting that the Defense Ministry’s report of radiation levels might be inaccurate. Publically available satellite imagery of the White Sea reveals the presence of the Serebyanka, a nuclear fuel vessel used to transport and retrieve cruise missiles after tests.

On August 9^th, regional Russian media report that pharmacies in Arkhangelsk and Severodvinsk are running out of iodine, which reduces the effects of radiation exposure, as residents spooked by Yudina’s now-censored statement rush to stock up. Authorities shut down shipping traffic in the area of the White Sea where the blast occurred for a month, without explaining why.

On Saturday, August 10^th, shortly after midnight, Rosatom, Russia’s state nuclear agency, releases a statement saying that five of its scientists were killed in an accident involving “isotopic sources of fuel on a liquid propulsion unit” that were tested on an “offshore platform.” The statement goes on to say that, “after the tests were completed, the rocket fuel was ignited, followed by detonation.”

On the same day, according to later reports from the Wall Street Journal, personnel with the Comprehensive Nuclear-Test-Ban Treaty Organization say that two radiation monitors near the site of the Russian accident went offline.

On Sunday, August 11, five officials from the nuclear institute where those who died in the blast worked confirm the accident in televised remarks. Vyacheslav Solovyov, the institute’s director, says his colleagues had been working on “the creation of small-scale sources of energy using radioactive fissile materials.”

On Monday, August 12, the five nuclear scientists are buried in a state funeral and accorded unspecified state honors.

On Tuesday, August 13, Rosgidromet issues a report via the official Tass newswire saying that radiation levels had risen by 4 to 16 times normal levels in Severodvinsk on August 8, the day of the accident. Yudina, the Severodvinsk spokeswoman, says that residents of the village of Nyonoksa would be evacuated for a two-hour window on August 14 in connection with unspecified work at the site. Local media instructs residents to take special trains that would be sent to their community, without saying when it would be safe to return. Yury Orlov, the Arkhangelsk regional governor later contracts that an evacuation has been ordered, calling it “complete nonsense.”

Meanwhile, two more radiation sensors in Northern Siberia go offline and stop transmitting data.

On Friday, August 16, The Moscow Times, an independent English-language newspaper, publishes anonymous interviews with Arkhangelsk area health care workers who say that they treated patients exposed to radiation the day the blast occurred. The sources, which include four doctors and a medical worker, say they were not told beforehand that the patients had been the victims of a radiation incident, which put hospital staff in danger. Although The Moscow Times’ sources didn’t directly treat the patients, they attended a briefing relative to the radiation hazard at the hospital. The medical workers tell the paper they were coerced by the Federal Security Service to sign non-disclosure agreements forbidding them to discuss the events.

On Monday, August 19^th, during a state visit to France, Vladimir Putin says there is no threat from the site of the explosion and that experts in the area of the White Sea are “controlling the situation” and that no “serious changes” have been reported.

On Tuesday, August 20th, Russian Deputy Foreign Minister Sergei Rybakov tells the Interfax news agency that Russia’s participation in sharing radiation information from its sensors is voluntary. Shortly thereafter the Associated Press reports that two of the radiation sensors that went offline begin transmitting data again.

On Wednesday, August 21^st, the independent Novaya Gazeta newspaper reports that two victims of the blast died of radiation sickness before they could be taken to Moscow for treatment. An unnamed worker who was involved in their care told the paper that: “Two of the patients did not make it to the airport and died. The radiation dose was very high, and symptoms of radiation sickness grew every hour.”

Later that day, Kremlin Spokesman Dmitry Peskov tells the Tass newswire that he has no knowledge of the incident. “I am not aware of it, I do not know what doctors you are talking about. It is necessary to know specifically what doctors are mentioned, who they are. In this case, we cannot speak impersonally,” he says.

Speaking in Helsinki, Putin confirms that the blast occurred during a weapons test. “This is work in the military field, work on promising weapons systems. We are not hiding this,” Putin says. “We must think of our own security.”

On Friday, August 23, Norway’s nuclear test-ban monitor reports that it has data indicating that the explosion in Nyonoska was followed by a second blast two hours later.

On Monday, August 26^th, Rosgidromet says that it had found the radioactive isotopes of strontium, barium and lanthanum in test samples taken after the explosion. Nuclear experts from Norway and the United States say this suggests that a nuclear reactor exploded in the August 8^th incident, rather than Rostaom’s vaguely described “isotope power source.”

On Tuesday, August 27^th, Norway’s nuclear test-ban monitor walks back its assertion that there were two explosions during the August 8^th accident, saying “Further analysis of the event with additional seismic data indicate that the event also may stem from mining activity in Finland.”

As of Wednesday, August 28^th, it remains unknown precisely what sort of nuclear device exploded in Nyonoksa on August 8^th and what were the radiation impacts ­– if any – on the victims of the blast and the population at large. What is clear is that there is far more to be known about this mysterious incident. What is less clear is whether Moscow will allow us to learn it.